bluuebunny/crossref_metadata_2025 huggingface dataset:
Triassic to Neogene geologic evolution of the Queen Charlotte region
Authors: Lewis P. D. , Haggart J. W. , Anderson R. G. , Hickson C. J. , Thompson R. I. , Dietrich J. R. , Rohr K. M. M.
Published: April 2011

A wealth of new geological and geophysical data from recent studies of the Queen Charlotte region are integrated into a coherent model. In this paper, we summarize these new studies and discuss possible correlations with other areas. Four tectonostratigraphic divisions are distinguished by stratigraphic, structural, and magmatic character, and each is separated by a major unconformity. The oldest division comprises widely distributed, upper Paleozoic through Middle Jurassic strata of Wrangellia that accumulated in volcanic-arc and stable shelf and basinal settings. No significant deformation occurred in the Queen Charlotte Islands region during the accumulation of these rocks. A Middle and Upper Jurassic assemblage comprises two plutonic suites and volcanic and epiclastic rocks. The unconformity below the Middle and Upper Jurassic assemblage marks a regional, southwest-vergent contractional deformation that is the most significant Mesozoic or Cenozoic deformation in the region. Jurassic plutons in the Queen Charlotte Islands are the oldest and most primitive members of an eastwardly migrating and evolving Jura-Cretaceous magmatic front recognized by other workers in the Coast Plutonic Complex. Widespread Late Jurassic block faulting led to differential uplift and erosion of northwest-trending fault blocks. A third assemblage consists of Cretaceous marine sedimentary rocks derived principally from subjacent Jurassic volcanic rocks as well as older strata. The present distribution of Cretaceous strata reflects a gradual eastward transgression, briefly interrupted in the Coniacian by progradation of conglomerate fans from the east. A second regional contractional deformation event in latest Cretaceous time was concentrated along a northwest-trending zone coinciding with Jurassic block faults. The early Tertiary marked another distinct shift in sedimentation style, with the inception of local nonmarine deposition on the present islands and widespread volcanism and plutonism on the southern islands. Syntectonic deposition in offshore extensional basins (Hecate Strait and Queen Charlotte Sound) may have commenced at this time. Later in the Tertiary, extensive deposition occurred in offshore regions, coeval with northward migration of plutonism and volcanism on the islands. Contractional structures in Pliocene sediments in Hecate Strait are the youngest deformational features observed.
Tectonic framework of the upper Paleozoic and lower Mesozoic Alava sequence: a revised view of the polygenetic Taku terrane in southern southeast Alaska
Authors: Rubin Charles M. , Saleeby Jason B.
Published: April 2011

Fragments of upper Paleozoic and lower Mesozoic metavolcanic and metasedimentary sequences of the Taku terrane are exposed discontinuously along a narrow belt in southeast Alaska and form a distinct lithostratigraphic package in the Ketchikan area called the Alava sequence. Crinoidal and argillaceous marble, carbonaceous phyllite, argillite, mafic flows, pillow breccia, pyroclastic tuff, and quartzite characterize the sequence. These strata are unconformably overlain by Upper Jurassic to Lower Cretaceous fine- to coarse-grained epiclastic rocks of the Gravina sequence. The upper Paleozoic part of the Alava sequence may be correlative with the Yukon–Tanana terrane, whereas the Middle and Upper Triassic portion of the Alava sequence may represent a metamorphic vestige of the Stikine terrane. Both parts are now exposed on the western flank of the Coast Plutonic Complex, in contrast with their correlatives to the east. These relations suggest that the Stikine and Alexander terranes were juxtaposed prior to deposition of the Gravina sequence. The western boundary between rocks of North American affinity and allochthonous ensimatic crustal fragments of the Alexander and Wrangellian terranes lies west of the Coast Plutonic Complex.
Evidence from aeromagnetics on the configuration of Matachewan dykes and the tectonic evolution of the Kapuskasing Structural Zone, Ontario, Canada
Authors: West Gordon F. , Ernst Richard E.
Published: April 2011

By digital image processing of federal–provincial aeromagnetic survey data for the south-central Superior Province, we have obtained an improved picture of the distribution of dykes in the huge Matachewan mafic dyke swarm (2454 Ma). We deduce from it a picture of post-emplacement deformation in the vicinity of the uplifted granulite gneisses of the Kapuskasing Structural Zone (KSZ). Matachewan dykes are emplaced in three subswarms. The two easterly subswarms are clearly truncated by the KSZ's eastern boundary faults. The western subswarm shows an open Z-bend as it crosses the KSZ, but it does not reveal any major fault offset. On the plausible assumption (supported by paleomagnetic data) that the subswarms were originally intruded radially, the horizontal strain suffered by the KSZ since emplacement of the dykes is mainly a northeast–southwest-trending band of dextral transcurrent deformation, which in the northeast is discontinuous and concentrated in a fault (horizontal offset 60–80 km) and in the southwest widens through a series of horsetail splays into an ~80 km wide zone of distributed strain. The KSZ is believed to have formed by a major, crustal-scale, thrust uplift along the KSZ's southeastern margin. Some thrusting is recorded by the dyke pattern, but this can account for only part of the ~20 km of differential uplift seen in the KSZ. Most likely, the mainly transcurrent deformation recorded by the dykes is a secondary event, and the primary period of thrust uplift predated dyke injection.
The Chazy Group, St. Lawrence Lowlands: anisotropy of magnetic susceptibility
Authors: Zhang Nan-Hai , Seguin Maurice-K.
Published: April 2011

Magnetic susceptibility (K) and anisotropy of magnetic susceptibility (AMS) were measured on 69 specimens from five sites in the Chazy Group of the St. Lawrence Lowlands in southern Quebec. The K values depict an isotropic to slightly anisotropic character. The AMS ellipsoid shapes range from oblate to prolate. The axes of minimum susceptibility (Kmin) are mainly perpendicular to the subhorizontal bedding, whereas the other two axes (Kmax) and (Kint) are subparallel to it and somewhat scattered. These observations suggest that the Chazy seafloor was a relatively stable sedimentary platform, with a rather flat bottom, and was a high-energy depositional environment. A cluster analysis indicates a predominant orientation of the Kmax axes in the north-northwest – south-southeast direction. Microscopic studies have shown that detrital magnetic minerals in some specimens align in that direction as well. It is thus inferred that this direction reflects the flow direction of paleocurrents. K was measured also at low temperature (in liquid nitrogen). The results show that the paramagnetic contribution to K is relatively well detected at very low temperature, but it is hampered by diamagnetic contributions to K at room temperature. The specimens contain very few primary ferromagnetic mineral carriers, and therefore the sedimentary rocks of the Chazy Group are not appropriate for standard paleomagnetic investigation.
Paleomagnetism of Quaternary and late Tertiary sediments on Mokowan Butte, southwestern Alberta
Authors: Barendregt R. W. , Irving E. , Karlstrom E. T.
Published: April 2011

Mokowan Butte in southwestern Alberta is capped by 32 m of unconsolidated sediment comprising five tills and their associated paleosols. Previous stratigraphic work has indicated that the older tills are probably Early Pleistocene to late Tertiary in age. Paleomagnetic studies, based on 125 samples, show that the uppermost till–paleosol unit and the modern subsoil are normally magnetized, whereas the till–paleosol units from the middle of the sequence have reversed magnetization. We argue that these belong to the Brunhes and Matuyama polarity zones, respectively. The lowest part of the sequence has not been studied in detail and is generally too coarse for paleomagnetic sampling, and samples that have been obtained contain no accurate record of the paleofield. These new data, together with those from Wellsch Valley in Saskatchewan, Banks Island in the Northwest Territories, Fort Selkirk in the Yukon, and Merritt in British Columbia, bring to five the number of early Quaternary sequences in Canada that have yielded a record of glacial sediments deposited during the Matuyama chron, and hence record glacial events prior to the last reversal of the geomagnetic field (720 ka).
Isotopic evidence for complex Pb sources in the Ag–Pb–Zn–Au veins of the Kokanee Range, southeastern British Columbia
Authors: Beaudoin Georges , Sangster D. F. , Godwin C. I.
Published: April 2011

In the Kokanee Range, more than 370 Ag–Pb–Zn–Au vein and replacement deposits are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks. The Kokanee Range forms the hanging wall of the Slocan Lake Fault, an Eocene, east-dipping, low-angle normal fault. The Pb isotopic compositions of galenas permit the deposits to be divided into four groups that form linear arrays in tridimensional Pb isotopic space, each group having a distinct geographic distribution that crosses geological boundaries. The Kokanee group Pb is derived from a mixture of local upper crustal country rocks. Ainsworth group Pb and Sandon group Pb plot along a mixing line between a lower crustal Pb reservoir and the upper crustal Pb reservoir. The Ainsworth group Pb isotopic signature is markedly lower crustal, whereas the Sandon group Pb is slightly lower crustal. The Bluebell group Pb plots along a mixing line between a depleted upper mantle Pb reservoir and the lower crustal Pb reservoir.The geographic distribution and the Pb isotopic composition of each group probably reflect deep structures that permitted mixing of lower crustal, upper crustal, and mantle Pb by hydrothermal fluids. Segments of, or fluids derived from, the lower crust and the upper mantle were leached by, or mixed with, evolved meteoric water convecting in the upper crust. Fracture permeability, hydrothermal fluid flow, and mineralization resulted from Eocene crustal extension in southeastern British Columbia.
Paleomagnetism of late Paleozoic rocks in the northern Cache Creek terrane near Atlin, British Columbia
Authors: Cole F. , Butler R. F. , Gehrels G. E.
Published: April 2011

The Cache Creek terrane is exposed along the length of the Canadian Cordillera and is composed of oceanic strata that are probably, at least in part, exotic to North America. In the northern portion of the Cache Creek terrane near Atlin, British Columbia, paleomagnetic samples were collected from layered Paleozoic rocks at 22 sites (≥ 6 samples/site) on Alfred Butte. Principal component analysis of detailed thermal demagnetization data allowed clear isolation of a characteristic remanent magnetization (ChRM) from 17 of these sites. Blocking temperatures to 680 °C indicate that this magnetization is carried by hematite, and site-mean ChRM directions are determined with α95 < 10° for the majority of sites. On Sentinel Mountain, samples were collected from 16 sites in layered Paleozoic volcanic and chert rocks and from a diabase sill. Thermal demagnetization revealed a ChRM in the chert and volcanic rocks with blocking temperatures to 680 °C, whereas alternating-field demagnetization to 40 mT successfully isolated ChRM in the diabase sill. ChRM directions from four sites involved in a mesoscopic S-fold at Alfred Butte fail the fold test, indicating that the ChRM is a postfolding secondary remagnetization. Tests for relative age of structural tilting and remagnetization are ambiguous, with attendant uncertainties in tectonic interpretations. However, rock-magnetic and geologic constraints argue for a chemical remagnetization of these Paleozoic rocks in Late Triassic to Middle Jurassic time, possibly associated with structural juxtaposition of the Cache Creek and Stikine terranes along the Nahlin fault zone. Although certainly nonunique and speculative, the simplest tectonic interpretation of these paleomagnetic data involves postfolding and posttilting remagnetization during the Early Jurassic in a paleolatitudinal position that approximately agrees with predicted North American paleolatitudes for this time.
Submarine sedimentary features on a fjord delta front, Queen Inlet, Glacier Bay, Alaska
Authors: Carlson Paul R. , Powell Ross D. , Phillips Andrew C.
Published: April 2011

Side-scan sonar images provide a view of an actively changing delta front in a marine outwash fjord in Glacier Bay, Alaska. Numerous interconnected gullies and chute-like small channels form paths for the transport of sand and coarse silt from the braided glacial outwash streams on the delta plain to the sinuous turbidity-current channels incised into the fjord floor. These turbidity-current channels carry coarse sediment through the fjord and into the adjoining glacial trunk valley. Several sedimentary processes affect the development of this delta front: overflow plumes deposit fine sediment; sediment gravity flows result from episodic delivery of large loads of coarse sediment; and mass movement may be triggered by earthquakes and, more regularly, by spring-tidal drawdown or hydraulic loading.
Lithostratigraphy and deep-water setting of the upper Nanaimo Group (Upper Cretaceous), outer Gulf Islands of southwestern British Columbia
Authors: England T. D. J. , Hiscott R. N.
Published: April 2011

The Upper Cretaceous Nanaimo Group consists of extensive shaly units and lenticular bodies of sandstone and conglomerate deposited in neritic to bathyal marine paleoenvironments. Single sandstone and conglomerate lenses cannot be traced throughout the basin, but instead tend to concentrate at particular stratigraphic levels, defining crudely sheet-like composite units of coarse-grained rocks. Many of the lenticular coarse-grained units rest in major channels, as deep as about 550 m. Sand and gravel were generally transported to the west and northwest by sediment gravity flows through these channels into the basin centre. Recognition of widespread channeling is critical to the definition of formal lithostratigraphic units (four formations and two informal members are defined here for the upper Nanaimo Group).The top of the Nanaimo Group is probably truncated by a major unconformity with local relief of at least 2 km. The effect of the unconformity can only be seen by mapping the orientation of offshore ridges in the Strait of Georgia, which can be traced into the sandstones and conglomerates above the inferred unconformity on Tumbo and Cabbage islands. Large scale cross-bedding, unidirectional paleocurrents, and lack of evidence for marine conditions favour a subaerial, fluvial setting for deposition of these rocks, which correlate to the lithologically similar Paleogene Chuckanut Formation on the Sucia Islands.
Atlas–axis complex of Secodontosaurus, a sphenacodontid mammal-like reptile (Eupelycosauria: Synapsida) from the Lower Permian of Texas
Authors: Reisz Robert R. , Scott Diane , Bendegem Jack van
Published: April 2011

The description of the atlas–axis complex of Secodontosaurus (an Early Permian synapsid) indicates that sphenacodontids share with primitive therapsids the derived feature of a tall atlantal pleurocentrum that extends to the ventral edge of the vertebral column. Although similar, the postcranial skeletons of Dimetrodon and Secodontosaurus can be differentiated by the distinct shape and size of the latter's axial neural spine and posterior zygapophysis.
Crustal structure of the Midcontinent rift system in eastern Lake Superior from controlled-amplitude analysis of GLIMPCE deep reflection seismic data
Authors: Samson C. , West G. F.
Published: April 2011

The reprocessing of line F of the GLIMPCE deep marine reflection seismic survey according to controlled-amplitude principles provides new insights on the crustal structure of the Midcontinent rift system in eastern Lake Superior. The insertion of refraction static corrections in the processing sequence was crucial to recover the lateral continuity and amplitude strength of reflectors under rough lake-bottom topography. Coherent noise consisting mainly of waves scattered by irregularities on die lake bottom and first-order water reverberations was best attenuated by use of multiple passes of velocity filtering in different seismic domains rather than by trace editing. Overall, the variations in reflection style and strength on our final stacked and trace envelope sections allow for the identification of broad geological domains. Lava flows and postrift sediments can be traced uninterrupted across most of the rift basin, which is bounded to the north by a complex region of secondary sagging, felsic volcanism, and (or) intrusives, and to the south by the Keweenaw fault. The crust–mantle transition zone is characterized by both a smooth amplitude anomaly and by discontinuous packages of diffractions and reflections. It is overlain by an anomalous transparent lower crustal domain beneath the central basin. These observations suggest that, during rifting, magma rose from a layer of underplated material located at the base of the crust to the surface through numerous small feeders. They do not, however, fully exclude die possibility of complete crustal separation.
Early Silurian carbonate platforms in the Appalachian orogenic belt: the Sayabec – La Vieille formations of the Gaspé–Matapédia basin, Quebec
Authors: Lavoie Denis , Bourque Pierre-André , Héroux Yvon
Published: April 2011

The coeval Early Silurian (late Llandoverian to late Wenlockian) Sayabec and La Vieille formations represent the first occurrence of shallow-water platformal limestones and reefs in the Paleozoic sequence of the Gaspé Belt of the northern Appalachians. Both units display very similar fades, representing laterally well-zoned, south-dipping carbonate platforms with four parallel depositional belts. These, from nearshore to offshore, are (i) a peritidal mud flat dominated by microbial communities (laminites, stromatolites, thrombolites, oncolites); (ii) a low knob reef rim built by skeletal metazoans (corals, bryozoans, stromatoporoids), skeletal calcareous algae, and microbial communities; (iii) a well-sorted lime sand belt; and (iv) a deeper water nodular lime mud belt supporting a tabulate and rugose coral, stromatoporoid, skeletal algae, and large-shelled brachiopod biota. The two platforms developed at the margin of the Quebec Reentrant and St. Lawrence Promontory in the Gaspé Belt of the northern Appalachian Orogen. It is not clear whether they were parts of a single continuous platform stretching along the northern margin of the Gaspé Belt or two separate platforms occupying distinct tectonic blocks. The development of the Sayabec and La Vieille platforms corresponds to the peak of the first shallowing phase in the Gaspé Belt after the Taconian orogeny. The platforms, with their reefs, grew during a period of sea-level stability from the earliest to late Wenlockian. The reefs were killed by an influx of deeper water siliciclastic sediments during a late Wenlockian transgression.
Terrane accretion in the internal zone of the Ungava orogen, northern Quebec. Part 2: Structural and metamorphic history
Authors: Lucas S. B. , St-Onge M. R.
Published: April 2011

The tectonic history of the early Proterozoic Ungava orogen is marked by structural–metamorphic episodes that both predate and postdate a collision between a magmatic arc terrane and the northern continental margin of the Superior Province. Distinct precollisional tectonic histories are documented for the rocks forming the lower plate of the Ungava orogen (the Archean Superior Province basement and an Early Proterozoic rift-to-drift margin sequence) and the orogenic upper plate (Early Proterozoic ophiolitic and magmatic arc units). The lower-plate units preserved in the external part of the orogen (Cape Smith Thrust Belt) record the development of a foreland thrust belt characterized by south-verging faults ramping up from a basal décollement located at the basement–cover contact. The plutonic core of the magmatic arc contains structures and metamorphic assemblages indicative of an episode of dextral transcurrent deformation contemporaneous with granulite-facies metamorphism and arc plutonism. The "tectonically suspect" ophiolitic and arc units were accreted to the thrust belt along south-verging faults, which reimbricated the foreland thrust belt and which resulted in at least 100 km of displacement of upper-plate units with respect to the autochthonous basement. Collisional thickening and consequent exhumation resulted in relatively high-pressure, greenschist- to amphibolite-facies metamorphism of lower-plate cover units, and in the retrogression of high-grade assemblages in the arc rocks. Postaccretion shortening resulted in folding of both the allochthonous rocks and the footwall basement.
Tip Top Hill volcanics: Late Cretaceous Kasalka Group rocks hosting Eocene epithermal base- and precious-metal veins at Owen Lake, west-central British Columbia
Authors: Leitch Craig H. B. , Hood C. T. , Cheng Xiao-Lin , Sinclair A. J.
Published: April 2011

Rocks hosting the Silver Queen epithermal Au–Ag–Zn–Pb–Cu vein deposit near Owen Lake, British Columbia, belong to the Tip Top Hill volcanics. They are lithologically similar to the informally named Upper Cretaceous Kasalka Group rocks exposed in the type area at Tahtsa Lake, 75 km southwest of the deposit, and at Mount Cronin, 100 km northwest of the deposit. The Kasalka Group rocks in the Tahtsa Lake area give questionable dates of 105 ± 5 Ma by K–Ar on whole rock but are cut by intrusions dated at 83.8 ± 2.8 Ma by K–Ar on biotite. The sequence at the Silver Queen deposit includes a polymictic conglomerate, followed upward by felsic fragmental rocks and a thick porphyritic andesite flow and sill unit, cut by microdiorite and quartz–feldspar porphyry intrusions. The porphyritic andesite and the microdiorite have been dated as Late Cretaceous (78.3 ± 2.7 and 78.7 ± 2.7 Ma, respectively, by K–Ar on whole rock), close to previous dates for these rocks (77.1 ± 2.7 and 75.3 ± 2.0 Ma, respectively). The quartz–feldspar porphyry intrudes the porphyritic andesites but has an older U–Pb zircon date of 84.6 ± 0.2 Ma, probably due to underestimation of the true age of the host rocks by the K–Ar whole-rock method. Later dykes correlate with younger volcanic rocks belonging to the Ootsa Lake and Endako groups. Eocene pre- and postmineral plagioclase-rich dykes (51.9 ± 1.8 to 51.3 ± 1.8 Ma) and late diabase dykes (50.4 ± 1.8 Ma; all by K–Ar on whole rock) may be correlative with trachyandesite volcanics of the Goosly Lake Formation, part of the Eocene Endako Group. These volcanics have been dated elsewhere at 55.6 ± 2.5 to 48.8 ± 1.8 Ma by K–Ar on whole rock and biotite, respectively. Mineralization at Silver Queen is therefore similar in age to, but slightly younger than, the producing Equity mine located 30 km to the northeast, which is estimated at 58.5 ± 2.0 Ma by K–Ar on whole rock.
Possible crustal contamination of Midcontinent Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin
Authors: Seifert Karl E. , Peterman Zell E. , Thieben Scott E.
Published: April 2011

Interlayered mafic–telsic intrusions from the Mineral Lake intrusive complex in northwest Wisconsin reflect the typical bimodal basalt–rhyolite compositional pattern of the Midcontinent Rift flood basalt province in the Lake Superior region. The later felsic intrusions were emplaced between the mafic intrusions and overlying basalt flows, and postemplacement fractional crystallization produced gradational mineralogical and geochemical variations. Isotopic and trace-element data for the Mineral Lake intrusions are consistent with mantle sources for both mafic and felsic intrusions, with compositional differences explained by the extent of fractional crystallization and crustal contamination or mantle source characteristics.εNd–εSr plots of analyzed Midcontinent Rift igneous rocks define three largely separate isotopic fields that suggest separate sources. However, the spread in isotopic data and a spider diagram plot of mafic samples from the εNd = εSr = 0 field suggest a crustal component and derivation from depleted rather than chondritic mantle. Evolved felsic rocks plotting in two negative εNd – positive εSr fields can be explained by derivation from separate enriched mantle sources or crustal contamination or both.
Crustal temperatures near the Lithoprobe Southern Canadian Cordillera Transect
Authors: Lewis T. J. , Bentkowski W. H. , Hyndman R. D.
Published: April 2011

Heat flow and radioactive heat generation have been measured and the data compiled across southern British Columbia in the region of the Lithoprobe Southern Canadian Cordillera Transect. Heat flow in the trench-arc zone between the continental margin and the Garibaldi volcanic belt is very low, but in the volcanic belt it is high and very irregular. Farther inland, to the east, the heat flow is moderately high, with the highest values in southeastern British Columbia, associated with high surface radioactive heat production. The thermal data from the central and eastern interior of southern British Columbia define a single heat-flow province with a reduced heat flow of 63 mW/m2 flowing into the upper crust. This indicates a warm, thin lithosphere similar to that of the Basin and Range of the United States to the south. Occurrences of seismic reflective bands in the lower crust of the Cordillera were compared with temperatures calculated from surface heat flow and heat generation using a simple one-dimensional conductive model. The 450 °C isotherm corresponds approximately to the brittle– ductile transition, and deeper crust may be rheologically detached from the upper crust. Where the thermal data approximately coincide with the transect seismic reflection lines, the 450 °C isotherm often corresponds to the top of characteristic sub-horizontal reflector bands, as found in Phanerozoic areas elsewhere around the world. The lower limit of the reflective band in a number of Cordilleran reflection sections is near the 730 °C isotherm, which corresponds to the transition from present "wet" amphibolite- to "dry" granulite-facies conditions. This control of the depth to the deep crustal reflective bands by present temperature provides support for the model of the reflectors being produced by fluids trapped at lithostatic pressure (layered porosity), a model that can also explain the high electrical conductivity in the deep crust of the area. The probable rheological detachment of the lower crust and a possible nonstructural origin of the deep reflectors require that interpreted lower crustal structural boundaries such as the top of the basement of the North American craton under the Lithoprobe Southern Canadian Cordillera Transect be treated with caution. However, there is no doubt that many seismic reflectors are related to crustal structures, and the model is presented as an explanation for bands of seismic reflectors in the lower Phanerozoic crust, not as a model for all seismic reflectors.
Paleomagnetism of the Keweenawan Chipman Lake and Seabrook Lake carbonatite complexes, Ontario
Authors: Symons D. T. A.
Published: April 2011

The Chipman Lake complex crops out as a series of carbonatite and related alkalic mafic dikes in the Wabigoon Subprovince of the Superior Province, whereas the Seabrook Lake complex crops out as an alkalic syenite – carbonatite stock in the Abitibi Subprovince. Paleomagnetic analysis was done on specimens from 23 and 19 sites located in and around the Chipman Lake and Seabrook Lake complexes, respectively, using detailed alternating-field and thermal step demagnetization and isothermal remanent magnetization tests. Contact tests with adjacent Archean host rocks show that both complexes retain a primary characteristic remanence (ChRM). The Chipman Lake's ChRM is retained in 11 dikes with normal polarity and one dike with reversed polarity and at one site with normal polarity and one site with reversed polarity from the fenite alteration zone. Its ChRM gives a pole position at 186°E, 38°N (dp = 7°, dm = 11°), which corresponds to a Keweenawan age of 1098 ± 10 Ma, suggesting that younger K–Ar amphibole ages do not date emplacement. The ChRM of the host rock, the Chipman Lake diorite stock, gives a pole at 49°E, 51°N (dp = 8°, dm = 13°), showing that it is not part of the Keweenawan complex but may be a 2.45 Ga Matachewan intrusive. The Seabrook Lake complex's ChRM is found at six normal polarity sites from within the complex and at four normal and three reversed polarity sites from within the fenitized Archean granite and Matachewan diabase of the contact aureole. It gives a pole position at 180°E, 46°N (dp = 11°, dm = 17°), which corresponds to a Keweenawan age of 1103 ± 10 Ma, agreeing with K/Ar biotite ages. The paleomagnetic data indicate that no significant motion on the Kapuskasing Structural Zone occurred after emplacement of the complexes excluding minor vertical uplift of less than about 4 km, and that there were multiple polarity transitions of a symmetric Earth's magnetic field during Keweenawan time.
Yapeenian (Early Ordovician) graptolites in the Quebec Appalachians
Authors: Maletz Jörg
Published: April 2011

A newly discovered Oncograptus upsilon fauna occurs in a sequence of turbiditic siltstones within the Lower Ordovician Ste-Anne River nappe in the Gaspé area of Quebec. This is the first discovery of true Yapeenian graptolites within the Canadian Appalachians. The fauna consists of O. upsilon, several subspecies of Pseudisograptus manubriatus (P. m. harrisi, P. m. janus, P. m. koi), and a variety of associated species.
The late Early Ordovician gastropod Teiichispira at Port au Port, Newfoundland
Authors: Yochelson Ellis L.
Published: April 2011

The operculum of Teiichispira odenvillensis has been mentioned in literature as occurring at Port au Port, western New foundland, but has not heretofore been documented. It is present in the lower part of the Aguathuna Formation along with opercula of Ceratopea unguis, another indicator of late Early Ordovician age. The rodlike construction, and subsequent fibrous appearance of this operculum when silicified, appears to be unique, making it readily identifiable in the field. Although Teiichispira has been closely allied with Maclurites, in part because each genus has a calcified operculum, the forms of opercula are sufficiently different that one may be dealing with a convergent adaptation, the heavy operculum adding weight to the animal and allowing it to live in more agitated waters.
Glacial Lake Mackenzie, Mackenzie Valley, Northwest Territories, Canada
Authors: Smith Derald G.
Published: April 2011

Glacial Lake Mackenzie, located in the middle reach of the Mackenzie Valley, extended 800 km as a long narrow lake between the Rabbitskin River, 50 km east of Fort Simpson, and the Ramparts cliffs near Fort Good Hope; part of the lake extended an additional 75 km west from the Ramparts. The lake averaged 15 km in width, but broadened to 75 km in the northern sector and 50 km near Fort Norman, and narrowed to 5 km near Wrigley. The depth was at least 80 m in the Fort Norman region and 60 m near Wrigley. Radiocarbon ages suggest that the lake had formed in the northwest by 11 760 BP, and that the last phase of the lake occurred in the south near Camsell Bend no later than 10 290 BP. The lake formed as a result of a bedrock (limestone) barrier at the Ramparts near Fort Good Hope and glacial depression of the basin. The demise of the lake is ascribed to outlet incision into the limestone barrier, sediment filling, and isostatic rebound. Differential postglacial rebound raised the Fort Simpson region at least 97 m higher than the Ramparts over the past 11 500 years.
Amphibole and plagioclase chemistry in two Proterozoic dyke swarms and its relation to the uplift history of the Kapuskasing Structural Zone
Authors: Palmer H. C. , Barnett R. L.
Published: April 2011

The gneisses of the Chapleau portion of the Kapuskasing Structural Zone (KSZ) and of the Wawa Gneiss Terrane (WGT) can be partitioned into subregions on the basis of magnetic polarity of 2.45 Ga Matachewan diabase dykes emplaced within them. West of the Ivanhoe Lake fault zone (ILFZ) the polarity sequence across the trend of the dyke swarm is normal–reverse–normal (N–R–N) over a traverse distance >100 km. Highly correlated with dyke N polarity is the presence of tea-coloured groundmass plagioclase and hornblende with high Al, Na, and Ti content. Reversely magnetized dykes within the WGT and in dykes of either polarity in regions far removed from the KSZ have groundmass plagioclase with hydrous alteration and relatively Al-poor amphiboles. Although N and R magnetized dykes have groundmass plagioclase with comparable Fe contents, the plagioclase of N dykes and Kapuskasing dykes in the highest grade country rock contain discrete, micrometre-sized, Ti-poor magnetite particles. The mineralogical variations are independent of whole-rock bulk chemistry and are ascribed to greater crystallization depth for N magnetized dykes. The magnitude of the amphibole compositional change in dykes at the western N–R boundary within the WGT is comparable to that across the ILFZ. The western N–R boundary is wholly within the WGT, whereas the ILFZ juxtaposes upper and lower crustal levels. As a consequence, only some of the differential uplift between the KSZ and the Abitibi belt can be accounted for in post-Matachewan dyke time. Limited data from the amphiboles in the 2.04 Ga east-northeast-trending Kapuskasing dykes suggest that this phase of faulting along these block boundaries postdates Kapuskasing dyke emplacement.
Silurian deformation in eastern Notre Dame Bay, Newfoundland
Authors: Lafrance Bruno , Williams Paul F.
Published: April 2011

Eastern Notre Dame Bay, Newfoundland, is divided into five fault-bounded terranes. They are, from north to south, the Twillingate Terrane, the Chanceport Terrane, the New World Island Terrane, the Dildo Run Terrane, and the Port Albert Terrane. The New World Island Terrane is characterized by fault-repeated sequences of Middle Ordovician to Early Silurian turbiditic sandstones (Sansom Formation) and conglomerates (Goldson Formation). The Chanceport Terrane has a lower volcanic unit and an upper sedimentary unit consisting of red and green siltstones–shales overlain by turdiditic sandstones. This sequence is structurally overlain by a mafic and felsic volcanic unit.The clastic sedimentary rocks of the Chanceport, New World Island, and Port Albert terranes best record the Silurian deformation in the area. Silurian deformation is divided into two deformation events: an Early Silurian D1 thrusting event and a Late Silurian D2 dextral ductile faulting event. The Early Silurian Joey's Cove Mélange constrains the age of D1 thrusting. Few small-scale fault ramps and intrafolial F1 folds are associated with D1 thrusting. Most penetrative deformation structures in eastern Notre Dame Bay formed during D2. Three fold generations (F2, F3, F4), the regional cleavage (S3), and tectonic mélanges are associated with D2 dextral ductile faulting. D2 structures overprint Early Silurian Goldson conglomerates, and are overprinted by Late Silurian to Early Devonian Loon Bay Suite intrusions. Devonian to Mesozoic brittle D3 faults cut across the ductile regional structures.Silurian deformation in eastern Notre Dame Bay began during the closure of the Iapetus Ocean when the Chanceport, New World Island, and Port Albert terranes, and possibly the Twillingate and Dildo Run terranes, were thrust towards the south over the Gander Zone. D2 dextral ductile faults formed to accommodate the nonorthogonal final closure of the Iapetus Ocean. The closure of the Iapetus Ocean in eastern Notre Dame Bay was oblique with a dextral horizontal component.
Effects of rifting and subsidence on thermal evolution of sediments in Canada's east coast basins
Authors: Dehler S. A. , Keen C. E.
Published: April 2011

Regional maps of lithospheric deformation and thermal history have been derived for the eastern continental margin of Canada. Subsidence associated with the rifting and cooling stages of rifted margin formation was calculated from gridded maps of sediment thickness and bathymetry along the Labrador, Grand Banks, and Nova Scotian margins. A two-layer lithospheric extension model was used to compute the deformation and thermal evolution of each region. Deformation results show that the crust and lower lithosphere have generally stretched by different amounts, and that either crustal or subcrustal lithospheric stretching dominates beneath the various basins. Thermal modelling results for the older Nova Scotian and Grand Banks margins show a strong correlation between thermal gradient, crustal stretching, and sediment thickness, and the predicted thermal gradient pattern for the younger Labrador margin correlates extremely well with predicted stretching of the still-cooling subcrustal lithosphere. Predictions of sediment maturity (vitrinite reflectance) of basin deposits were obtained from the derived time – temperature histories. Model results have been constrained with observations from individual boreholes and extrapolated away from these well-constrained areas into regions beyond the frontiers of present exploration. Results are presented as maps showing depths to present-day peak thermal maturity zones and the ages at which earliest post-rift sediments reached peak maturity levels. This reconnaissance approach has led to predictions of thermal maturity zones suitable for oil or gas generation in western Orphan Basin and beneath the continental slopes.
Postglacial and pre-last-glacial weathering of till on the high plateaus of central Gaspésie, Quebec, Canada
Authors: Bédard Pierre
Published: April 2011

Geochemical data from mineral exploration surveys are used to assess postglacial and pre-last-glacial weathering on the high plateaus of central Gaspésie by comparing the distribution of 30 elements in the B and C horizons of a thin soil developed on glacial deposits. Under postglacial weathering, Fe2O3, TiO2, P2O5, Cr, Li, U, and V are immobile relative to Al2O3, whereas the other elements are mobile and have been depleted to various degrees from the B horizon. Loss-on-ignition value is the only parameter showing a significant enrichment from the C to the B horizons. The apparently high degree of geochemical weathering of the glacial deposits in respect to their source bedrock lithologies suggests that the deposits also contain previously weathered material. The spatial distribution of the geochemical weathering index values calculated for the C horizon shows no clear relation to the underlying bedrock formations. The high values are located on topographic highs, with maxima over deeply weathered bedrock occurrences, and the low values are located in glacial valleys. The spatial distribution of this weathering index in the glacial deposits shows the geochemical signature of a pre-last-glacial weathered mantle.
Genèse du gaz naturel de la région de Trois-Rivières, basses terres du Saint-Laurent, et de Saint-Flavien, Appalaches, Québec, Canada
Authors: St-Antoine P. , Héroux Y.
Published: April 2011

Isotopic analyses of 13C and 2H concentrations in methane and determinations of the total gas molecular composition were completed on five samples collected in the Pleistocene sediments of the Trois Rivières area, St-Lawrence Lowlands, and of the Saint-Flavien area, in the Appalachians, where accumulations of natural gas occur. The results indicate that (i) the gas at Yamachiche is biogenic and formed in situ within the Pleistocene deposits, (ii) the gas at Saint-Flavien is thermogenic, and (iii) the gas at Pointe-du-Lac and at the Vieilles-Forges is likely a mixture of both. The petrogenic study of the organic matter of the Beekmantown Group, Middle Ordovician age, suggests that the gas at Saint-Flavien migrated into the present reservoir after the thermal peak. [Journal Translation]
Origin of the Late Devonian Weekend lamprophyre dykes, Meguma Zone, Nova Scotia
Authors: Tate M. C. , Clarke D. B.
Published: April 2011

The Weekend dykes consist of 10 Late Devonian spessartite lamprophyres cropping out within the allochthonous Meguma lithotectonic terrane of the northern Appalachians. The dykes have characteristic panidiomorphic textures, with seriate phenocrysts of amphibole, clinopyroxene, and rare biotite set in a groundmass of intergrown plagioclase, K-feldspar, and quartz, with deuteric calcite and epidote. All dykes intruded during one magmatic episode (ca. 370 Ma) following terrane accretion of the Acadian Orogeny. The unaltered Weekend dykes show restricted major element variation (SiO2 54–58 wt.%, Al2O3 14–16 wt.%, MgO 7–11 wt.%, and total alkalies 2.4–5.5 wt.%) and have high Mg# (71–80) and moderate to high concentrations of Ni (69–278 ppm) and Cr (390–992 ppm). Large ion lithophile element (e.g., Sr, Ba 294–1194 ppm) and light rare earth element (13–67CN) abundances are high relative to high field strength element (e.g., Nb, Ta, Y 0.45–26 ppm) and heavy rare earth element (6–30CN) abundances. Geochemical variation largely corresponds to minor phenocryst fractionation, but high Mg# indicate the primitive nature of most dykes and preclude significant evolution of lamprophyric magmas in the crust. Incompatible element enrichments coupled with depleted mantle high field strength element abundances probably require a melt derived from reenriched lithospheric mantle sources, whereas Nb depletion and the volatile-rich mineralogy suggest metasomatic contributions from subducted ocean lithosphere. Geochemical comparisons with continental margin arc basalts and immobile element tectono-magmatic discrimination reinforce a subduction model for the Weekend dykes and strongly suggest active subduction prior to the emplacement of the Meguma terrane.
Pétrologie du granite peralcalin du lac Brisson, Labrador central, Nouveau-Québec. II. Minéralogie et modalités de cristallisation
Authors: Pillet D. , Chenevoy M. , Bélanger M.
Published: April 2011

Mineral zonation in the Québec–Labrador Brisson Lake peralkaline granite displays quartzose and feldspathic lithofacies arranged concentrically, the latter occupying the centre of the intrusion. The zonation is the result of successive magmatic pulses. In the feldspathic facies, agpaitic crystallization began under hypersolvus conditions around 720 °C with PF = 0.1 GPa. Subsolvus crystallization involving enrichment of the residual liquid in F continued to below 500 °C. The quartzose facies is more differentiated and its composition was controlled by feldspar fractionation. Early quartz crystallization is partly explained by the high content of F in the magma. The mafic mineral succession is, in both facies: Li- and Zn-rich arfvedsonite with an important ferrorichtérite component, which crystallized along with alkali feldspar under low [Formula: see text]; aenigmatite contemporary of amphibole or anterior, destabilized to form neptunite, astrophyllite, aegirine, or arfvedsonite; primary titaniferous aegyrine, contemporary with the amphibole and replaced by secondary aegyrine; neptunite and astrophyllite replacing aenigmatite. This succession is in accordance with the increase of Na and F in the fluid phase, and the increase of [Formula: see text] near the end of crystallization. Among the accessory minerals, euhedral zircon is indicative of the initial richness of the magma in Zr. Magmatic vlasovite, and elpidite formed from late fluid, are evidence that residual system entered the zirconium silicate stability field. Zircon with a fibrous, radiating texture, and gittinsite are indicative of the postmagmatic evolution of the pluton and the presence of a late stage residual fluid which was enriched in Ca and Sr.
Appalachian basement and its intrusion by Cretaceous dykes, offshore southeast Nova Scotia, Canada
Authors: Jansa L. F. , Pe-Piper G. , Loncarevic B. D.
Published: April 2011

Aeromagnetic data collected between eastern Nova Scotia and southern Newfoundland provide new information about the offshore extension of the Avalon and Meguma terranes. A zone of short-wavelength anomalies that delineates Scatarie Ridge extends westward to the Late Proterozoic Fourchu Group in southeastern Cape Breton Island and eastward towards the Burin Peninsula of Newfoundland, suggesting that both regions belong to the same tectono-stratigraphic province of the Avalon composite terrane. A different zone of short-wavelength, discontinuously lineated anomalies at the northern edge of the Canso Ridge correlates with amphibolite-facies metamorphic rocks of the Meguma terrane on the Canso Peninsula, interpreted as an exhumed deeper metamorphic level of the Meguma terrane at its boundary with the Avalon terrane. The S-shaped pattern of long linear magnetic trends, characteristic of lower grade Meguma rocks on the southern flank of the Canso Ridge, indicates plastic deformation of the Meguma terrane during the Acadian orogeny when emplaced against the rigid Cape Breton Island block indentor. Analogous patterns occur off western Nova Scotia, suggesting little strike-slip motion occurred between the Meguma and Avalon terranes since the Acadian orogeny.Late Proterozoic rocks on Scatarie Ridge are intruded by Cretaceous diabase dykes. The diabase is alkaline with a within-plate geochemical signature, similar in composition to basalt flows in the Orpheus half-graben. A depleted-mantle model age TDM (Nd) of 731 Ma, εNd = +6.5, suggests that the magma was sourced from a lithospheric mantle reservoir involved in Late Proterozoic magmatic activity. Aeromagnetic data interpretation confirms the distribution of Cretaceous basalt flows and sills within Mesozoic sedimentary strata of the Orpheus half-graben previously outlined by seismic methods but was unable to differentiate between Proterozoic and Mesozoic intrusive rocks where the Proterozoic rocks lay near to the ocean floor.
Deep structure beneath Lake Ontario: crustal-scale Grenville subdivisions
Authors: Forsyth D. A. , Milkereit B. , Zelt C. A. , White D. J. , Easton R. M. , Hutchinson D. R.
Published: April 2011

Lake Ontario marine seismic data reveal major Grenville crustal subdivisions beneath central and southern Lake Ontario separated by interpreted shear zones that extend to the lower crust. A shear zone bounded transition between the Elzevir and Frontenac terranes exposed north of Lake Ontario is linked to a seismically defined shear zone beneath central Lake Ontario by prominent aeromagnetic and gravity anomalies, easterly dipping wide-angle reflections, and fractures in Paleozoic strata. We suggest the central Lake Ontario zone represents crustal-scale deformation along an Elzevir–Frontenac boundary zone that extends from outcrop to the south shore of Lake Ontario.Seismic images from Lake Ontario and the exposed western Central Metasedimentary Belt are dominated by crustal-scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east-dipping linear reflections. The images show that zones analogous to the interpreted Grenville Front Tectonic Zone are also present within the Central Metasedimentary Belt and support models of northwest-directed crustal shortening for Grenvillian deep crustal deformation beneath most of southeastern Ontario.A Precambrian basement high, the Iroquoian high, is defined by a thinning of generally horizontal Paleozoic strata over a crestal area above the basement shear zone beneath central Lake Ontario. The Iroquoian high helps explain the peninsular extension into Lake Ontario forming Prince Edward County, the occurrence of Precambrian inlier outcrops in Prince Edward County, and Paleozoic fractures forming the Clarendon–Linden structure in New York.