bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Canadian 1.9 Ga old continental crust. I: Nd isotopic data
Authors: Chauvel C. , Arndt N. T. , Kielinzcuk S. , Thom A.
Published: April 2011

A Nd isotopic study was carried out on 1.9−1.8 Ga rocks from two parts of the Trans-Hudson Orogen in northern Canada. The first part is the Reindeer Lake Zone in the Churchill Province in Saskatchewan, where a variety of volcanic, granitoid, and sedimentary rocks are preserved in several lithotectonic belts that border a reworked Archean craton to the northwest. The second area comprises the Ottawa and Belcher islands, in Hudson Bay, and the Fox River volcanics, in Manitoba. These form part of the Circum-Superior Belt, a band of basaltic volcanics and sedimentary rocks that overlies the Archean Superior craton.From U–Pb zircon ages, Pb–Pb ages, and Sm–Nd ages, Nd initial isotopic compositions were calculated for all analyzed samples. In the Saskatchewan terrains, we obtained a large range of εNd values, from +5 to −8. The highest values (+4 to +5) come from two volcanic-dominated belts (Flin Flon and Western la Ronge), lower values (~+2) characterize intervening sediment-dominated domains (Eastern La Ronge, Glennie Lake, and Kisseynew), and still lower values (−1 to −4) were found in migmatitic and granitoid belts adjacent to the reworked Archean craton in the northwest. Each lithotectonic belt has its own characteristic, restricted range of εNd values, and, with few exceptions, there is no correlation between εNd and rock type; i.e., in individual belts, volcanics, granites, and sediments have very similar εNd values.In the Circum-Superior Belt, three lava flows from the Ottawa Islands have εNd values ranging from +4.5 to 0, and samples from the Belcher Islands have values ranging from +3.5 to −9.These results are explained by mixing between mantle-derived rocks and variable amounts of Archean continental crustal rocks. Assuming that 1.9 Ga ago the mantle had an εNd value of +5 and Archean crust had an εNd value of −12, we calculate proportions of Archean crustal material in Trans-Hudson rocks ranging from ~2 to 35 %, increasing systematically toward the Archean platform. The mean Archean component is about 8%: this area of Proterozoic continental crust is clearly dominated by material derived directly from the mantle.The similarity between the εNd values of sediments, granites, and volcanics in the Trans-Hudson Orogen suggests that sedimentary processes played a dominant role in transporting Archean detritus from eroding Archean continental areas into basins, where it mixed with mantle-derived volcanic material and melted to form granitoids.
Graptolites from the Lower–Middle Ordovician St. George and Table Head groups, western Newfoundland, and their correlation with trilobite, brachiopod, and conodont zones
Authors: Williams S. Henry , Boyce W. Douglas , James Noel P.
Published: April 2011

Faunal assemblages of the autochthonous, shelf carbonate sequences belonging to the St. George and Table Head groups are dominated by shelly macrofossils and conodonts. Rare, usually monotypic graptolitic horizons enable correlation with the allochthonous Cow Head Group, which was deposited on the middle to lower slope, and the shelly, conodont, and graptolitic zonal schemes elsewhere in North America.The Catoche Formation of the St. George Group is of Ibexian (Canadian) age and yields graptolites indicative of the Tetragraptus approximatus and Tetragraptus akzharensis zones (early Arenig). The basal Aguathuna Formation belongs to the Pendeograptus fruticosus Zone, whereas higher parts span the Ibexian–Whiterock boundary. Graptolites suggest that the Table Head Group entirely postdates the Cow Head Group. This is supported by a Whiterock (early Llanvirn) trilobite, conodont, and brachiopod fauna.
Upper Triassic sponges (Sphinctozoa) from southern Yukon, Stikinia terrane
Authors: Senowbari-Daryan Baba , Reid R. Pamela
Published: April 2011

The first Tethyan-type Upper Triassic sponge reefs in North America have recently been discovered in the southern Yukon, in Stikinia terrane. Sphinctozoa from these reefs and inter-reef limestones are represented by 18 species and 12 genera belonging to six families. The genus Yukonella with one species, Y. rigbyi, and the species Polytholosia ramosa and Polycystocoelia norica are described for the first time. Some of the Yukon sponges were previously known only from the Tethyan realm (Colospongia, Dictyocoelia, Polycystocoelia, and Uvanella?); others, from Tethyan and North American localities (Ascosymplegma, Follicatena, Paradenigeria, and Salzburgia?). One (Polytholosia cylindrica) is probably endemic to North America. The mixed affinities of the Yukon sponges may reflect the paleogeographic origin of Stikinia as an island in the ancestral Pacific Ocean, between Tethys and the North American craton.
Deglaciation of Chilliwack River valley, British Columbia
Authors: Saunders Ian R. , Clague John J. , Roberts Michael C.
Published: April 2011

Quaternary sediments and landforms in Chilliwack River valley, southwestern British Columbia, provide a detailed record of déglaciation of this area between 12 000 and 11 000 years BP. Stratigraphic, sedimentological, and radiocarbon data show that a large glacier in eastern Fraser Lowland (part of the Cordilleran Ice Sheet) blocked the mouth of Chilliwack valley at a time when the middle reaches of the valley were ice free. A lake existed between the ice dam in the lower part of the valley and a delta – sandur complex, west of Chilliwack Lake, in the upper part of the valley. Two relatively minor advances of the Fraser Lowland ice lobe into lower Chilliwack valley occurred about 11 500 and 11 200 years BP. These were separated by a brief period of recession during which tephra was deposited and a coniferous forest and soil developed on freshly deglaciated terrain. Shortly after 11 200 years BP, a glacial lake formed in Cultus Lake basin; two sets of terraces in lower Chilliwack valley are graded to different levels of this lake. The glacier dam at the mouth of Chilliwack valley disappeared about 11 000 years BP, and déglaciation of Fraser Lowland was complete less than 100 years later.
Electron spin resonance dating of tooth enamel
Authors: Grün Rainer , Schwarcz Henry P. , Zymela Steve
Published: April 2011

The amplitude of the electron spin resonance (ESR) peak at g = 2.0018 for hydroxyapatite of fossil tooth enamel can be used to measure the acquired radiation dose (AD) and thus the time (T) since burial of the tooth in a sediment. No significant fading or saturation occurs up to at least 1 Ma, permitting dating of middle Pleistocene deposits. AD is determined by the additive-dose method, using a sufficiently large modulation amplitude to avoid the interference of organic free radicals, and a logarithmic transformation of the ESR intensity to correct for saturation effects. AD increases through time as a result of (1) constant irradiation by U, K, and Th in the surrounding sediment and by cosmic rays; (2) external irradiation by beta particles from U in the dentine; and (3) alpha and beta particles from U in the enamel. We derive an expression for AD(T) taking into account (1) approach to equilibrium between U and its long-lived daughters; and (2) T-dependent (early or linear) uptake of U by dentine or cement and by enamel, as well as the constant environmental radiation sources. T is determined by iteratively solving this expression to obtain the observed AD. An example is given of the dating of an elephant tooth from a preglacial deposit in Alberta: the calculated age is consistent with assignment to isotope stages 5c–5e.
Geochemistry of two Cretaceous coal-bearing sequences: James Bay lowlands, northern Ontario, and Peace River basin, northeast British Columbia
Authors: Flier-Keller E. Van der , Fyfe W. S.
Published: April 2011

Cretaceous coal-bearing sequences from the Moose River basin in northern Ontario and the Peace River basin in northeast British Columbia were analysed for trace- and major-element contents. Modes of occurrence of the trace elements are proposed on the basis of Pearson correlation coefficients and scanning electron microscopy coupled with energy-dispersive X-ray analysis.The Moose River basin lignite was deposited in an alluvial floodplain environment, and the restricted mineralogy, dominated by quartz and kaolinite, reflects derivation from a highly weathered terrain. The bituminous coal from the Peace River basin was deposited in an alluvial to deltaic environment, with a dominant mineralogy including quartz, illite, kaolinite, mixed-layer clays, carbonates, barite, feldspar, and pyrite.Trace-element contents in both deposits are comparable to the average concentration in United States coals. Modes of occurrence of trace elements in the coals are extremely variable and depend on local conditions both during deposition and subsequently. Association with the organic matter is the most common mode of occurrence of trace elements in the Moose River basin lignites, whereas clay minerals are important trace-element sites in the Peace River basin coal.Factors including coal rank, clay mineralogy, nature of the surrounding rocks, and composition of the groundwaters appear to have important influences on the concentrations of the trace elements and their siting in the coals.
Depositional controls on the magnetic characteristics of lodgement tills and other glacial diamict facies
Authors: Eyles N. , Day T. E. , Gavican A.
Published: April 2011

Genetic interpretation of massive, unstructured diamict and diamictite facies is a commonly encountered problem faced by sedimentologists. Data are presented concerning the magnetic characteristics, namely, anisotropy of magnetic susceptibility (AMS) and natural remanent magnetism (NRM) of facies deposited by (1) lodgement processes at a glacier base (lodgement till) and (2) subaqueously by pelagic mud deposition and ice-rafting ("rain-out" diamicts). Lodgement tills have an NRM that is distorted around the geomagnetic pole position to form a girdle approximately 90° in length, either transverse or parallel to ice flow direction. This distension appears to be the result of subglacial shear processes because other diamicts, deposited passively by melt-out below stagnant ice and modelled by a laboratory experiment, show a nondeformed NRM clustering around the geomagnetic pole. The AMS data show that lodgement tills have only a weakly orientated magnetic microfabric.Glaciolacustrine "rain-out" diamicts show a precise NRM clustering as in marine and lacustrine muds. This reflects the lack of nongeomagnetic forces acting upon magnetic grains during deposition followed by postdepositional remanence "locking" at depth in the sediment column. These facies show both random AMS fabrics, typical of undisturbed pelagic sediments, and preferred microfabrics resulting from local sediment flow on the lake floor.It is concluded that NRM and AMS offer considerable assistance in genetic studies of massive diamict facies; AMS is particularly useful because the large populations of samples can be rapidly processed. The wider use of this technique by sedimentologists—for investigating other sedimentary facies types—is anticipated.
A proposed model for the formation of reversely zoned plutons based on a study of the Lacorne Complex, Superior Province, Quebec
Authors: Bourne James , Danis Daniel
Published: April 2011

The Lacorne Complex is a calc-alkaline mass of Archean age located in the Abitibi region of Quebec. The complex can be subdivided into three zones. The inner zone varies in composition from hornblende > biotite gabbro breccia to monzonite, with all rocks containing ≤ 5 % modal quartz. The outer zone rocks contain more than 5% modal quartz and range in composition from biotite > hornblende quartz diorite to granodiorite. The third zone, consisting of muscovite–biotite–garnet leucomonzogranite, is exposed only in the northwestern portion of the complex. The transition between each zone is relatively abrupt but continuous. Based on 400 modal estimates of stained slabs and 107 whole-rock and trace-element analyses, it is demonstrated that both the inner zone and the outer zone rocks are reversely zoned: mafic cores are surrounded by more felsic borders. Various methods that could explain the observed geochemical trends are considered. The data indicate that crystal–liquid equilibria were maintained during crystallization and that mechanisms such as magma mixing can be rejected. A two-stage model involving sidewall crystallization and upwelling of fractionated magma accumulating near the roof of the magma chamber is proposed to explain the reverse zoning.
The Nicola Group: Late Triassic and Early Jurassic subduction-related volcanism in British Columbia
Authors: Mortimer N.
Published: April 2011

Mafic lavas of the Nicola Group are divided into three distinct petrographic and geochemical types: type 1 lavas are strongly augite-porphyritic picrites, basalts, and andesites that belong to a high-potassium to shoshonitic rock series; type 2 lavas are augite- and plagioclase-porphyritic basalts and andesites that belong to a low-potassium calc-alkaline series; and type 3 lavas are petrographically variable tholeiitic to transitional basalts and andesites.Low concentrations of Ti, Zr, Y, and Nb and moderate to high concentrations of K, Rb, Ba, and Sr in type 1 and 2 lavas clearly indicate a subduction-related tectonic setting of eruption. Type 3 lavas show chemical affinities intermediate between modern-day island-arc and intraplate volcanics. Type 1 (shoshonitic) lavas generally lie east of and are younger than type 2 (calc-alkaline) lavas, a relationship that implies an east-dipping early Mesozoic subduction zone beneath the Nicola arc. These interpretations resolve previous uncertainties regarding the tectonic setting of eruption of the Nicola Group.Several major 205–220 Ma plutons that intrude the Nicola Group crystallized from type 1 and 2 magmas and represent the final stages of Late Triassic to Early Jurassic arc-related igneous activity in southern Quesnellia.
Field, isotopic, and chemical studies of tourmaline-bearing rocks in the Belt–Purcell Supergroup: genetic constraints and exploration significance for Sullivan type ore deposits
Authors: Beaty David W. , Hahn Gregory A. , Threlkeld William E.
Published: April 2011

The Sullivan Pb–Zn–Ag massive sulphide deposit (located in the mid-Proterozoic Belt–Purcell Supergroup near Kimberley, British Columbia) is associated with a large tourmalinite alteration zone. A petrologically similar, but barren, alteration zone has recently been discovered at Trestle Creek, Idaho. Because of the importance of the Sullivan deposit, several methods of exploration involving tourmaline have recently been proposed in the literature. To test these proposals, we compared the alteration zone at Sullivan (using literature data) with that at Trestle Creek. The two areas can clearly be distinguished using Mg content in tourmaline and δ18O in albitite, can probably be distinguished using δ18O in tourmaline-bearing rocks, but cannot be distinguished using alteration mineralogy alone. In addition we found that tourmaline occurs in at least eight different geologic settings in the Belt–Purcell Supergroup (one of which includes the alteration zones at Sullivan and Trestle Creek).Assuming a high water/rock ratio, a moderate to very high degree of oxygen-isotope exchange, and a hydrothermal fluid with δ18O ≥ 0, a series of hydrothermal models can be calculated for the alteration zones at Sullivan and Trestle Creek. The most realistic models at both localities involve temperatures of about 200–250 °C and fluids of marine derivation with a variable 18O shift. The isotopic differences between Sullivan and Trestle Creek are probably the result of a greater degree of fluid evolution and higher temperatures at Sullivan. Oxygen isotopes, hydrogen isotopes, and mineral chemistry of tourmaline from other geologic settings in the Belt–Purcell Supergroup suggest deposition from fluids of marine origin under various temperature conditions.
Stratigraphy, depositional setting, and tectonic significance of the clastic cover to the Fidalgo Ophiolite, San Juan Islands, Washington
Authors: Garver John
Published: April 2011

The San Juan Islands of northwest Washington State comprise a diverse assemblage of Paleozoic and Mesozoic terranes amalgamated during a regional Cretaceous orogenic event. Detailed tectono-stratigraphy of the sedimentary cover to the Fidalgo Complex indicates the presence of several stratigraphically distinct units, which are described and formalized in this paper. The Fidalgo Complex and its sedimentary cover are the structurally highest rocks in the San Juan thrust system.The Fidalgo Complex is a highly disrupted Middle to Upper Jurassic ophiolite with arc-related intrusives, volcanics, and sediments. The Trump unit is an informally named sequence of siliceous sediments, volcanic graywacke, and minor volcanics that occurs at the stratigraphically highest portion of the Fidalgo Complex. Complex facies, lithologies, and provenance indicate that deposition of this Oxfordian(?) to upper Tithonian unit occurred in an arc-proximal setting.The upper Tithonian and younger Lummi Group (elevated here) lies depositionally above the Fidalgo Complex; locally the contact is an angular unconformity. The James Island Formation (new) is designated as a lower unit of the Lummi Group in the Decatur Island area. The chert-rich volcaniclastic sediments of the James Island Formation, locally containing ophiolitic debris, represent submarine-fan deposition within a tectonically active basin where basement blocks were uplifted along fault scarps.Middle Cretaceous thrusting and lawsonite–prehnite–aragonite metamorphism predated deposition of the Obstruction Formation (new), which is inferred to unconformably overlie the Lummi Group – Fidalgo Complex. Metamorphism postdated the late Albian, as rocks of this age are metamorphosed. The Obstruction Formation (?Cenomanian–Turonian) does not have metamorphic lawsonite–prehnite–aragonite, which are characteristic of underlying terranes in the San Juan Islands. Instead, the Obstruction Formation contains clasts derived from underlying metamorphosed terranes in the San Juan Islands; some clasts show these high-pressure, low-temperature metamorphic minerals. The Obstruction Formation probably represents synthrusting sedimentation that occurred after the San Juan terranes were metamorphosed and rapidly brought to the surface by continued thrusting over a hanging-wall obstruction. Thrusting was most likely driven by the accretion of Wrangellia against the North American margin.
Precise U–Pb zircon dates from the Avalon Terrane in Newfoundland
Authors: Krogh T. E. , Strong D. F. , O'Brien S. J. , Papezik V. S.
Published: April 2011

The following new U–Pb dates are provided for zircons from volcanic and intrusive rocks of the Avalon Terrane of Newfoundland: Burin Group ophiolite (Wandsworth pegmatitic gabbro), [Formula: see text]; Marystown Group ash-flow tuff, [Formula: see text]; Rock Harbour Group rhyolite clast in conglomerate, [Formula: see text]; Harbour Main Group ash-flow tuff, [Formula: see text]; Harbour Main Group flow-banded rhyolite, [Formula: see text]; porphyritic rhyolite plug intruding Harbour Main Group, 632 ± 2 Ma; Holyrood Granite, [Formula: see text]; rhyolite dyke, Harbour Main Group, [Formula: see text]; and welded ash-flow tuff, "Grand Beach porphyry," [Formula: see text]. All of the dated zircons are simple, single-age populations with no trace of inheritance. These dates confirm that the ophiolitic Burin Group represents an older and separate event that correlates precisely with the Bou Azzer ophiolite of Morocco and that the Rock Harbour Group does not represent continental volcanism that preceded that event. The Rock Harbour, Marystown, and Harbour Main groups and the Holyrood Granite (632–608 Ma) are all part of the younger 650–550 Ma pulse of Pan-African orogenesis that affected a broad area extending through Africa, Asia, western Europe, southern England and Wales, and eastern North America. However, a shortage of high-precision dates throughout these terranes precludes very exact correlations and thus very exact interpretations in terms of specific tectonic or magmatic events. Although these dates require some revisions in the stratigraphy of the Newfoundland Avalon Terrane, they do not support suggestions that the Avalon Terrane comprises a "collage of suspect terranes." The age of the Grand Beach porphyry (394 Ma) places it squarely with the Acadian granites of the Appalachians and removes it from consideration as part of the Marystown Group.
Lingulid brachiopods and Lingulichnus from a Silurian shelf–slope carbonate sequence, Delorme Group, Mackenzie Mountains, Northwest Territories
Authors: Over D. Jeffrey
Published: April 2011

Structures assigned to the ichnogenus Lingulichnus, commonly containing the burrow-forming brachiopod, were collected from an argillaceous unit in a Silurian shelf dolostone sequence (Delorme Group). The sediments, benthic fauna, and inclined orientation of all lingulid burrows indicate the presence of a bottom current and restricted conditions on the margin of the Selwyn Basin. High-abundance–low-diversity faunas of lingulids and Lingulichnus are indicative of limiting conditions at the substrate surface. Under low-energy conditions, they seem to be indicative of the Zoophycos ichnofacies.
Mise en évidence d'un provincialisme chez les chitinozoaires ordoviciens
Authors: Achab Aïcha
Published: April 2011

A palynological study of the Ordovician of Quebec has revealed the characteristics of chitinozoan assemblages that lived in regions occupying a low-latitude position. The composition of these assemblages is distinctly different from that of assemblages of the same age described from southwest Europe and North Africa and occupying a higher latitude position.
Unreworked Archaean basement and Proterozoic supracrustal rocks from northeastern Disko Bugt, West Greenland: implications for the nature of Proterozoic mobile belts in Greenland
Authors: Kalsbeek F. , Taylor P. N. , Pidgeon R. T.
Published: April 2011

Whole-rock Rb–Sr and Pb–Pb and zircon U–Pb isotope data yield an age of approximately 2800 Ma for the Atâ granite from northeastern Disko Bugt, West Greenland. Field observations and isotope data suggest that the surrounding gneisses were formed by deformation and recrystallization of granitoid rocks similar to the Atâ granite some 100 Ma after the emplacement of the granite. Rb–Sr whole-rock data on siltstones at low metamorphic grade give an age of 1760 ± 185 Ma, which is interpreted as the time of closure of the isotope systems after metamorphism. The initial 87Sr/86Sr ratio demonstrates that the sediments were probably deposited during the early Proterozoic.Field observations and isotope data show that Proterozoic (Hudsonian s.l.) deformation and metamorphism were weak in the investigated area. The Archaean basement is well preserved, and the metasediments have well-preserved sedimentary structures. The area lies between the Proterozoic Nagssugtoqidian and Rinkian mobile belts of West Greenland, which are thus separated by an area of Archaean rocks little affected by mid-Proterozoic tectono-thermal events. Thus the two belts form separate tectonic units and do not constitute a single contiguous vast area of Archaean rocks reworked by Proterozoic deforma-tion and metamorphism. It is suggested that the Proterozoic mobile belts of West Greenland are orogenic zones of restricted width (a few hundreds of kilometres) that may be interpreted in terms of modern plate tectonic processes.
Drift carbonate on the Canadian Shield. II: Carbonate dispersal and ice-flow patterns in northern Manitoba
Authors: Dredge L. A.
Published: April 2011

In northern Manitoba, carbonates were glacially dispersed westwards for distances up to 260 km beyond the limit of carbonate bedrock. The dispersal pattern in the surface till reflects the interaction of Keewatin and Hudson – Labrador ice in the region during the Wisconsin glaciation and suggests the presence of ice streams within the Laurentide Ice Sheet. Pre-Wisconsinan tills show different dispersal and ice-flow patterns. In unfrozen terrain, carbonate till sheets on the Shield buffer the effects of natural lake acidification and acid rain; however, their ability to buffer appears to be severely limited in permafrost terrain.
Emplacement age of the Cross kimberlite, southeastern British Columbia, by the Rb–Sr phlogopite method
Authors: Smith C. B. , Colgan E. A. , Hawthorne J. B. , Hutchinson G.
Published: April 2011

The Cross kimberlite diatreme, located in the Columbia Mountains, southeastern British Columbia, has an emplacement age of 240–250 Ma, obtained by the Rb–Sr method on phlogopite. The time of emplacement was earlier than the intensive eastward structural displacements that occurred in this part of the Canadian Cordillera during the Laramide Orogeny, and the kimberlite may be structurally displaced as well as dismembered at depth.
The first record of the mosasaur Hainosaurus (Reptilia: Lacertilia) from North America
Authors: Nicholls Elizabeth L.
Published: April 2011

Hainosaurus pembinensis, a new species of tylosaurine mosasaur, is described from the Pembina Member of the Pierre Shale (Campanian, Late Cretaceous) of Manitoba. Hainosaurus differs from Tylosaurus in having a larger number of vertebrae anterior to the chevron-bearing caudals, a greater length of the femur relative to the humerus, and a greater length of the external nares. Hainosaurus pembinensis is distinguished from other species of this genus by its long supratemporal fenestra and homodont dentition. This is the first record of Hainosaurus from North America and represents both a geographic and stratigraphic range extension for the genus.
Regional imbrication within Quesnel Terrane, central British Columbia, as suggested by conodont ages
Authors: Struik L. C.
Published: April 2011

Quesnel Terrane, at Quesnel Lake, consists of two regional Triassic–Jurassic age-equivalent units, the Takla–Nicola and Slocan – King Salmon assemblages, as determined from conodonts and macrofossils. The upper mainly volcanic unit (Takla–Nicola) overlies the mainly pelitic unit (Slocan – King Salmon) and was probably emplaced by thrusting. The lower unit consists of dark grey pelite, siltite, limestone, and lesser amounts of fragmental basalt and greywacke. The upper unit consists of fragmental basalt, diorite, greywacke, and lesser amounts of dark grey siltite and pelite and limestone. The unit age and stacking order suggest that during the Jurassic, the volcanic-rich thrust sheet was transported northeastward over an eastern, more pelitic facies of the terrane. The northwesterly trending thrust trace is approximately 300 km long. The Triassic and Lower Jurassic subduction-generated volcanic unit may have been deposited on sediments and volcanics equivalent to the upper Paleozoic Harper Ranch Group; the eastern Triassic and Lower Jurassic pelite unit may have been deposited on the pillow basalt and ribbon chert of the upper Paleozoic Slide Mountain Group. The upper Paleozoic Harper Ranch and Slide Mountain group rocks may have rested on attenuated North American crust.
La marée d'inclinaison à Leduc (Alberta), Canada : observation, analyse et interprétation
Authors: Rouleau Pierre , Rogers James S. , Jones F. Walter
Published: April 2011

In geophysics the signal resulting from tidal forcing is the only one precisely known a priori. Its omnipresence in tilt measurements can be exploited to characterize the spatio-temporal properties of rocks in situ but only if experimental uncertainties are less than 2%. Signal distortions due to unknown material and geometrical discontinuities around sensors limit the observational accuracy. Tilt tides were measured with a new biaxial tiltmeter installed in a 12 m borehole at Leduc, Alberta, where the geology is well defined both locally and regionally. At the M2 frequency, the observed parameters (error of 2–5%) are coherent with results previously obtained with near-surface tiltmeters installed 100 m away but 5 times noisier. The load tide due to oceans differs according to which configuration is used in its computation, and the new measurements favor Schwiderski's M2 model over that of Parke and Hendershott. A topographic perturbation due to a small valley at 500 m from the borehole has been identified by comparing the tilt residuals for M2 and O1 with the strain tide. The results indicate that even a smooth topography can perturb tidal observations to the point of hampering the interpretation of tilt anomalies in terms of regional tectonics.
Proterozoic metamorphism in the Grenville Province: a study in the Double Mer – Lake Melville area, eastern Labrador
Authors: Gower C. F. , Erdmer P.
Published: April 2011

A regional metamorphic gradient from upper greenschist to granulite facies is identified south of the Grenville front in the Double Mer – Lake Melville area of eastern Labrador. Mineral assemblages in politic–granitic gneiss, amphibole-bearing quartzo-feldspathic gneiss, and coronitic metagabbro allow three major metamorphic domains to be established. These are collectively divisible into 11 subdomains. Geothermobarometry applied to the higher grade domains suggests that each is characterized by specific P–T conditions, which achieved 1000–1100 MPa and 700–800 °C in the deepest level rocks.The problem of reconciling geochronological data (which record a major orogenic event at 1650 Ma) with the occurrence of high-grade mineral assemblages in 1426 Ma metagabbro (which suggests a pervasive Grenvillian event) is discussed in terms of three models. The preferred model envisages crustal stabilization at 1650–1600 Ma to give high-grade mineral assemblages seen in the host rocks and with which mineral assemblages in coronitic metagabbro equilibrated after their emplacement at 1426 Ma. During Grenvillian orogenesis (1080–920 Ma) the present structural configuration was achieved by thrust stacking. This imparted a sporadic metamorphic and structural overprint and Grenvillian ages in selected accessory minerals.
Upper Llandovery and Wenlock graptolites from Prairie Creek, southern Mackenzie Mountains, Northwest Territories
Authors: Lenz Alfred C.
Published: April 2011

A moderately rich fauna of graptolites, comprising species dominated by Monograptus (sensu stricto), Retiolites, Stomatograptus, and Cyrtograptus is documented from Prairie Creek, southern Mackenzie Mountains, Northwest Territories. Graptolites of the upper Llandovery Monograptus turriculatus, Monograptus spiralis, and Cyrtograptus sakmaricus zones and of the Wenlock "unnamed zone" and Cyrtograptus rigidus and Monograptus testis – Cyrtograptus lundgreni zones are recognized. The species composition of these zones is significantly different from corresponding zones elsewhere in the Canadian Cordillera.Twenty-six species are described and illustrated, and of these, two are new: Stomatograptus canadensis and Cyrtograptus preclarus; and two species, Monograptus aff. riccartonensis and Cyrtograptus aff. sakmaricus might also be new. Several species, particularly Monograptus praecedens, Monograptus veles, and Monograptus cf. mutuliferus strigosus have not been prevously reported in North America.
Petrology and pyroxene chemistry of Monteregian dykes: the origin of concentric zoning and green cores in clinopyroxenes from alkali basalts and lamprophyres
Authors: Bédard Jean H. J. , Francis Don M. , Ludden John
Published: April 2011

The Mesozoic Monteregian alkaline province of southern Quebec includes mafic alnöite, monchiquite, basanite, camptonite, and alkali basalt dykes. Most carry phenocrysts of clinopyroxene that generally zone towards Ti–AlIV–Fe–Mn-rich and Mg–AlVI–Cr-poor rims. The zoning can best be explained through polybaric crystallization and differentiation during ascent from the upper mantle. In intermediate and leucocratic dykes, clinopyroxene AlIV–Ti contents decrease with the Mg/(Mg + ΣFe) ratio, probably reflecting concurrent fractionation of a Ti-rich phase. Pyroxene phenocrysts in Monteregian mafic dykes commonly have green clinopyroxene cores that are richer in Na and Fe and poorer in Mg and Cr than the enclosing titansalite phenocrysts. Some cores are euhedral and sector zoned, implying crystallization from a melt more evolved than their present hosts. The high AlVI contents of these cores imply high pressures of crystallization. The abundance of crustal xenoliths and evolved pyroxene cores indicates that the host magmas hybridized with felsic melts, cumulates, or metasomatites within the crust or an anomalously Fe–Na-rich upper mantle. This implies that the host dykes are not primary magmas but hybrids. Consequently, dyke chemistry cannot simply be inverted to determine the composition and mineralogy of the mantle source.
Strain-induced mineral growth in ductile shear zones and a preliminary study of ductile shearing in western Newfoundland
Authors: Piasecki M. A. J.
Published: April 2011

In the Fleur de Lys and the Central Gneiss terranes the presence of strain-induced mineral growth characteristic of ductile shear zones within zones of rocks with mylonitic fabrics indicates the existence of major belts of layer-parallel ductile shearing with complex evolutionary sequences. Kinematic markers in several of these shear belts indicate that shearing movements on initially probably gently inclined surfaces, directed not normal to the axial trend of the orogen but parallel to it, are tectonically important in western Newfoundland. The shear belts are in excess of 1 km thick, and one well-exposed example exhibits a pattern in which zones of the highest strain anastomose on the map scale.The base of the Fleur de Lys Supergroup is marked by one such major zone of shearing (décollement) in which kinematic indicators record movements directed to the north and to the south, before the regional attitude of the rocks was steepened. Along the Baie Verte Line, earlier north- and south-directed movements in the Fleur de Lys were succeeded by reverse movements towards the east, over the Dunnage Terrane.
Mineralogy and geochemistry of an Archean tuffaceous exhalite: the Main Contact Tuff, Millenbach mine area, Noranda, Quebec
Authors: Kalogeropoulos Stavros I. , Scott Steven D.
Published: April 2011

The Main Contact Tuff, in the vicinity of Millenbach mine, Noranda, Quebec, is an extensive, although discontinuous, ore-related volcanic exhalative metalliferous sediment, or "tuffaceous exhalite," of Archean age. It was formed by the variable contribution of two constituents: (1) exhalite (chemical) composed mainly of pyrite, quartz, sphalerite, pyrrhotite, and chalcopyrite and (2) tuff (clastic) composed of quartz, chlorite, and sericite.Tuffaceous exhalites such as the Main Contact Tuff and the similar tetsusekiei of the Japanese Kuroko deposits (Miocene age) indicate a fossil hydrothermal system that may or may not have produced economic concentrations of metallic sulfides. The Main Contact Tuff displays cryptic variations, which provide exploration guides at different scales: (1) the Fe/[Fe + Mg] ratios of chlorite decrease from 0.63 to 0.32 over a distance of 0.3 km approaching ore from the north, and from 0.72 to 0.32 over 1.5 km from the south; (2) the FeO/[FeO + MgO] (sulfide-free) ratios of whole-rock specimens decrease from about 0.8 to 0.3 approaching the ore; (3) ilmenite is replaced in the ore zone by rutile and (or) sphene; and (4) the most manganiferous ilmenite is found close to ore. On the other hand, trace elements of exhalative origin (e.g., Ag, Co) in the Main Contact Tuff appear not to provide useful vectors towards ore. They are concentrated relative to normal pelagic rocks, but their distributions with respect to ore are complicated by multiple input sources and postexhalative redistributions of elements.
Geometric relationship between the Scrip Nappe and metamorphic isograds in the northern Adams River area, Monashee Mountains, British Columbia
Authors: Sevigny James H. , Simony Philip S.
Published: April 2011

In the northern Adams River area of the Monashee Mountains, British Columbia, the axial trace of the Scrip Nappe, a megascopic southwest-verging recumbent F1 anticline, can be traced upward through all stratigraphic units of the Late Proterozoic Horsethief Creek Group westward to where it is truncated by the Eocene North Thompson Fault. The Scrip Nappe has been coaxially folded by a northeast-verging, isoclinal F2 synform with a southwest-dipping axial surface and an amplitude of about 6 km. A metamorphic culmination, defined by the surface trace of the muscovite-out isograd and consisting of a series of northwest–southeast-striking isogradic antiforms and synforms, postdates Early Cretaceous F2 folding and predates Eocene normal faulting at 51–45 Ma.
Sedimentology of an Archean submarine channel-fill deposit in the Abitibi greenstone belt of Canada
Authors: David Jean , Lajoie Jean
Published: April 2011

The Archean La Bruère Formation, which forms part of the Timiskaming Group of the Abitibi greenstone belt of Rouyn–Noranda, comprises a conglomerate–sandstone assemblage at least 360 m thick. The upward variations in grain size and con glomerate/sandstone ratio permit subdivision of the formation into three conglomeratic and two sandy members. Member 1 is composed essentially of conglomerate; members 2 and 4 consist of stacked composite beds of conglomerate and sandstone; member 3 is a sequence of cross-bedded sandstone. The formation is capped by a turbidite sequence (member 5).Three bed types (facies) were identified in the La Bruère Formation: two are restricted to the conglomerate; the third, to the upper member. Facies A, is characterized by matrix-supported, poorly sorted gravel beds, massive or reversely graded. In facies B, generally restricted to member 4, the conglomerate is commonly clast supported and transitional with the overlying sandstone bed, forming couplets that show primary structure sequences consisting, from base to top, of (i) normally graded gravel, (ii) plane-bedded sandstone, and (iii) cross-bedded sandstone. These sequences are similar to, although coarser and thicker than, some sequences found in turbidites. Facies C, observed only in member 5, is characterized by classic turbidites.In the conglomerate members of the formation, beds of facies A show no correlation between bed thickness and maximum grain size, whereas those of facies B show a fairly good correlation. The absence of correlation could result from accumulation in a channel rather than on an alluvial fan, but it may also be due to the nature of the flows responsible for the deposit and (or) the grain availability at the source.The characteristics of the three facies suggest that the La Bruère gravel accumulated from laminar and turbulent mass flows in a subaqueous channel, below storm wavebase and therefore in a relatively deep basin.
Formation de phyllosilicates dans les roches carbonatées cristallines de La Mauricie, Québec
Authors: Kimpe Christian de
Published: April 2011

The chemical and mineralogical analyses of the disaggregated material collected in the fracture planes of crystalline carbonate outcrops at three sites north of Trois-Rivières, Quebec, showed the formation of expanding phyllosilicates, smectite and vermiculite, mainly at the expense of the ferromagnesian minerals hornblende and augite. The clay minerals are enriched in Fe and Mg with respect to the parent material composition and are associated with the crystalline Fe oxides goethite and lepidocrocite. The moderate to low degree of mineral transformation is accounted for by the slow dissolution of the carbonates. Corrensite, a regularly interstratified clay mineral, was identified in 50% of the samples; it probably resulted from the hydrothermal alteration of phlogopite. Silicate alteration may have been responsible for a fraction of the swelling minerals found in the soils of the area.
A geodynamic model for extension in the Shuswap core complex, southeastern Canadian Cordillera
Authors: Ranalli G. , Brown R. L. , Bosdachin R.
Published: April 2011

The Shuswap core complex records Mesozoic and Paleocene crustal shortening with superimposed Eocene extension. During the shortening phase the crust was thickened and slowly uplifted. Within at most 20 Ma of the climax of compression, the crustal welt was rapidly uplifted and tectonically denuded.Shortening of the continental crust may be balanced in the underlying lithosphere by thickening or underplating, forming in either case a lithospheric root beneath the crustal welt. We consider a model whereby Tertiary crustal extension in the Shuswap core complex, and possibly also in other segments of the North American Cordillera, is accounted for by the detachment of this root. Both the time frame and the stress field resulting from the detachment are compatible with geological and geophysical observations. Far-field stresses played an accommodating role, but the potential energy required for extension of the Shuswap complex was induced by lithospheric thickening.
Petrogenesis of mantle-derived, LILE-enriched Archean monzodiorites and trachyandesites (sanukitoids) in southwestern Superior Province
Authors: Stern Richard A. , Hanson Gilbert N. , Shirey Steven B.
Published: April 2011

In southwestern Superior Province, diorite, monzodiorite, and trachyandesite ("sanukitoids") occurring within syn- to post-tectonic intrusive complexes and within greenstone belts have the following chemical characteristics: 55–60 wt.% SiO2, MgO > 6 wt.%, Mg# > 0.60, Ni and Cr both > 100 ppm, Na2O + K2O = 6 wt.%, Sr and Ba both 600–1800 ppm, and rare-earth-element (REE) patterns that are strongly light rare-earth-element (LREE) enriched (Cen = 80–250, Ybn = 4 – 10) and show no Eu anomalies. Sanukitoids and their granodioritic derivatives constitute at least 5% of the exposed crust in the study area. The sanukitoids cannot be derived by melting, fractionation, or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids. Crustal contamination of komatiites fails to explain the high large-ion-lithophile-element (LILE) contents of the sanukitoids. Rather, we suggest that the sanukitoids were derived by hydrous melting of LILE-enriched mantle peridotite at pressures between 10 and 15 kbar. The sanukitoids with steepest REE patterns have the lowest FeO contents, indicating that the part of the mantle source with the highest Mg# had the most fractionated REE pattern prior to melting. Mantle source regions to the sanukitoids had different Mg#'s and were enriched in LILE's (metasomatized) to varying extents by fluids of crustal or mantle origin prior to melting.
Late Proterozoic stratigraphy, U–Pb zircon ages, and rift tectonics, Mackenzie Mountains, northwestern Canada
Authors: Jefferson C. W. , Parrish R. R.
Published: April 2011

Stratigraphic evidence suggests sporadic rifting began during deposition of the mainly platformal Mackenzie Mountains Supergroup: minor magnetite iron-formation in shale basins, lead–zinc in karsted and brecciated carbonates, red-bed and evaporite wedges, and basalts at the top. In the unconformably overlying Coates Lake Group similar climates and definite rifting are recorded by thin orthoconglomerates with thick red-bed and evaporite wedges containing stratiform copper deposits in paleovalleys. Unconformably above this, basal Windermere Supergroup records major climatic change and more emphatic rifting, with thick orthoconglomerates next to fault scarps overlain by glaciomarine deposits with volcanics and hydrothermal iron-formation.A quartz diorite plug, here dated by the U–Pb zircon method at [Formula: see text], is bounded by faults but is contained in a thrust panel together with Mackenzie Mountains Supergroup and is chemically similar to diabase sills previously dated at 766–769 ± 27 Ma (Rb–Sr). A diatreme intruding Coates Lake Group contains clasts of granite and gneiss from inferred basement. U–Pb systematics from a granite clast indicate inherited zircons about 1.6 ± 0.25 Ga in age and crystallization between 1100 and 1175 Ma, a maximum age for Mackenzie Mountains Supergroup.
Paleohydrology of a Canadian Shield lake inferred from 18O in sediment cellulose
Authors: Edwards T. W. D. , McAndrews J. H.
Published: April 2011

Oxygen- and carbon-isotope analyses on cellulose in the postglacial sediment of Weslemkoon Lake, southern Ontario, show that the cellulose came mainly from aquatic plants or algae, rather than from terrestrial sources. If a wholly aquatic source is assumed, the oxygen-isotope content permits inferences of lake-water δ18O values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis. Chronological control is provided by pollen analysis and six 14C dates. Our reconstruction shows lake-water δ18O fluctuated from about 5‰ lower than present in the early postglacial to 5‰ or more above present values during the mid-postglacial. These broad, secular shifts reflect a combination of fluctuating mean annual δ18O of local precipitation, evaporative isotopic enrichment of surface waters, and snowmelt-bypass effects. The first two factors reflect the changing paleotemperature and paleohydrology, respectively, whereas the third factor is a more speculative interpretation of isotope effects during snowmelt delivery to the lake. The snowmelt-bypass mechanism is supported by parallel changes in the overall abundance and seasonal distribution of precipitation. This effect is probably responsible for pronounced isotopic enrichment of the water throughout the moist climate of the past 6000 years.
The role of microorganisms in phytokarst development on dolostones and limestones, Grand Cayman, British West Indies
Authors: Jones Brian
Published: April 2011

Phytokarst is spectacularly developed on the hard, finely crystalline dolostones of the Oligocene–Miocene Bluff Formation and to a lesser extent on the soft limestones of the Pleistocene Ironshore Formation on Grand Cayman. The black weathered surfaces, which are a reflection of an organic coating, contrast sharply with the white colour of the unaltered host rocks, which lack an organic coating. On the dolostones this organic coating is formed principally of fungal(?) sporangia and spores associated with mucilage along with lesser numbers of algae and bacteria. Endolithic and epilithic filamentous microorganisms are rare. On the limestones the organic coating is formed principally of endolithic and epilithic filaments and mucilage. Fungal(?) spores are rare, and no sporangia were found. The limestones of the Ironshore Formation are characterized by an intensely bored zone beneath the weathering surface. In contrast, the dolostones of the Bluff Formation have relatively few endoliths penetrating from the weathering surface.Dolomite rhombs on the weathered surfaces of the Bluff Formation are severely etched with well-developed rhomb-shaped etch pits, have holes through them, or have one or more of their faces removed and their cores partly leached. The dissolution of these crystals appears to be related to surface reaction-controlled kinetic processes mediated by the organic coatings. In contrast, the surfaces of the limestones do not display any of the delicate etch topography and appear to be dissolved at a much faster rate.Although both the limestones and dolostones are undergoing similar surface-weathering processes there are important, but subtle, differences in which those processes are operating. A critical factor in this contrast is the hardness of the substrate. The hard dolostones have a rich, diverse epilithic flora but poor endolithic flora, whereas the softer limestones have a relatively poor, low-diversity epilithic flora but abundant endoliths.