bluuebunny/crossref_metadata_2025 huggingface dataset:
Applications of digital methodology to the NATMAP Shield Margin Project
Authors: Broome H John , Viljoen David
Published: April 2011

The NATMAP Shield Margin Project, which began in 1991, straddles the Manitoba-Saskatchewan border and studied a rectangular area with east-west and north-south extents of approximately 250 and 150 km, respectively. Among the principal objectives of the NATMAP program were a compilation of a digital geoscience database for the study area and development of digital methodology to build this database and its utilization to aid in reaching the geological goals of the project. It was anticipated that these initiatives would encourage integrated interpretation of data, improve the effectiveness of the geological mapping process, and accelerate publication of results. One of the keys to effectively applying digital methods to a geological mapping project is maintaining data in digital form throughout the project, from the field through to publication. Transcription errors are eliminated and the production of both preliminary and final maps and digital products is accelerated. Access to digital data also facilitates application of digital tools for analysis and visualization. Integrated image products generated from geophysical and geological data sets were used throughout the project and assisted in development of geological models and their visualization. Three-dimensional visualization methods were used to combine NATMAP surface and subsurface mapping with Lithoprobe interpretations of seismic reflection data. The digital database was used to prepare a digital archive of the project which will be published in CD-ROM after completion of the project.
Maastrichtian-Paleocene foreland-basin stratigraphies, western Canada: a reciprocal sequence architecture
Authors: Catuneanu Octavian , Sweet Arthur R
Published: April 2011

Palynological and magnetostratigraphic chronostratigraphic correlations of lower Maastrichtian to Paleocene strata along an east-west Western Canada Basin transect allow for the recognition of a reciprocal sequence architecture in nonmarine strata. Reference sections include three Canadian Continental Drilling Program Cretaceous-Tertiary Boundary Project core holes and outcrops in Alberta, southern Saskatchewan, and north-central Montana. The spatial and temporal position of the third-order sequences provides evidence for the correlation of proximal sector regional disconformities and sedimentary wedges with distal sector sedimentary wedges and regional disconformities, respectively. The boundary between the two sectors is represented by a hingeline, which separates the foreland-basin "syncline" from the "peripheral bulge." The stratigraphies defined by reciprocal third-order sequences are complicated by fourth-order boundaries, developed within proximal sedimentary wedges and with no correlative distal strata. These results support tectonic control on foreland-basin sedimentation. A model for interpreting the various types of sequences in terms of foreland-basin evolution, vertical tectonics, and orogenic cycles is provided. It is argued that nonmarine sequence boundaries (times of maximum uplift in the foreland region) may be expressed as disconformities, incised valleys, top of mature paleosol levels, or base of fluvial channels, whereas nonmarine equivalents of marine maximum flooding surfaces (times of maximum basinal subsidence) may be indicated by extensive coal seams and (or) lacustrine sediments.
A late Coniacian ceratioid dinoflagellate cyst, Odontochitina octopus sp.nov., from the Kanguk Formation, Canadian Arctic
Authors: Núñez-Betelu K , Hills L V
Published: April 2011

Anew species of dinoflagellate cyst, Odontochitina octopus sp.nov., is described from the Upper Cretaceous Kanguk Formation of the Sverdrup Basin, Canadian Arctic Islands. The features that support the proposal of this new species also necessitate the emendation of the genus. Odontochitina octopus is a large, cornucavate, and ceratioid cyst with four finger-like terminations on the apical horns and two terminations on both the postcingular and antapical horns. These finger-like terminations are unique to this new species and are formed by the detachment of the paraplates at mid-length of each horn. All other features of O. octopus conform with the previous description of the genus. In the Family Ceratiaceae four plates form the apical horn, whereas two plates are involved in both the postcingular and antapical horns. In O. octopus the mid-length detachment of the horn-forming paraplates seems to have developed the finger-like terminations. Since the nature and amount of pores and perforations in other species of Odontochitina are variable and possibly linked to changes in the environment, the presence of the multiple-fingered O. octopus in a single widespread horizon might also be indicative of short-lived unusual environmental conditions. At this horizon, which has been dated as late Coniacian by the ammonite Scaphites depressus Reeside, the palynomorph assemblage is highly dominated by marine species.
Thermal maturity and burial history of Paleozoic rocks in western Newfoundland
Authors: Williams S Henry , Burden Elliott T , Mukhopadhyay P K
Published: April 2011

Palynomorphs and graptolites from Paleozoic strata in western Newfoundland are examined and correlated with previously published data to identify fossils which are characteristic of proven and suspected source rocks. Measurements of colour alteration of acritarchs and spores (acritarch alteration index and thermal alteration index), random graptolite reflectance, and vitrinite reflectance are applied to determine regional thermal maturation and burial history. General trends of increasing maturity from south to north along the Northen Peninsula and from west to east across the Port au Port Peninsula are observed. Within these general trends, a more detailed distribution of thermal maturities can be recognized. In the south, Upper Ordovician rocks of the Long Point Group, western Port au Port Peninsula, exhibit the lowest maturity values found in western Newfoundland and are considered immature or marginally mature. Middle Ordovician rocks of the Goose Tickle and Table Head groups and the Lower Ordovician St. George Group are marginally mature. Cambrian strata on the Port au Port Peninsula are mature. Maturation levels increase to the east; Goose Tickle Group black shales in the vicinity of Black Cove, east of Port au Port, are mature. Equivalent sediments extending for another 15-20 km to the east lie within the oil window. Beyond that area, the equivalent rocks are overmature. The best potential source rocks belonging to the allochthonous Cow Head Group contain abundant acritarchs and Gloeocapsamorpha sp. These rocks are marginally mature to mature within Gros Morne National Park; maturation levels increase farther north (e.g., Parsons Pond), becoming overmature somewhere south of Port au Choix. It is concluded that neither the allochthonous Ordovician rocks presently exposed in Gros Morne nor the autochthonous strata exposed on the Port au Port Peninsula have ever been covered by significant thicknesses of overburden (probably 3 km or less), either in the form of structural slices or other sedimentary units since their original deposition.
Ice foot, freeze-thaw of sediments, and platform erosion in a subarctic microtidal environment, Manitounuk Strait, northern Quebec, Canada
Authors: Allard Michel , Michaud Yves , Ruz Marie-Hélène , Héquette Arnaud
Published: April 2011

The role of shore ice and freeze-thaw processes in intertidal sediments was studied along the inner shoreline of Manitounuk Strait through a series of drillings through the ice foot and numerous observations at all seasons. Mechanical processes such as drift-ice scouring and clast transport play only a minimal part in the observed changes. The thermal behaviour of the ice foot and the control it exerts on surface and groundwater flow throughout winter are the dominant factors of the shoreline dynamics. As the ice foot freezes to the surface of the tidal flat, a freezing front penetrates to depths of 3 m in the underlying sediments, which consist of postglacial Tyrrell Sea clays. This induces the formation of segregation ice which destroys the structure of the clays and leads to their thaw liquefaction in early summer. As this deep penetration of frost beneath the ice foot also impedes winter groundwater and surface-water flow, forced seepage and springs form icings (naleds), frost blisters, and lens-shaped bodies of intrusive ground ice at the upper margin of the tidal zone. The melting of all this ground ice induces settlement, microcliff collapse, and mud flows. The Manitounuk tidal zone, rather than being a typical tidal flat, is an erosional platform that is cut in soft Quaternary sediments and is being graded to tidal regime. Freeze-thaw processes controlled by the presence and thermal behaviour of the ice foot are the principal agents of platform destruction while waves and tidal currents are the transport agents that remove the sediments from the tidal zone. Platform erosion is presently the main source for sediment deposition in the shallow waters of Manitounuk Strait. Such a series of coastal periglacial processes may play an important role in other subarctic coastal settings. They also play an important ecological role, as they prevent the colonization of the coastal zone by mollusks and restrict the extent of coastal marshes.
Pridoli graptolites from northern Xinjiang, Northwest China
Authors: Ni Y -n , Lenz A C , Chen X
Published: April 2011

Integration of graptolite dates obtained from two sections in northern Xinjiang, Northwest China, permits the recognition of one Pridoli biostratigraphic zone, the Monograptus bouceki Biozone. Graptolites described from the biozone comprise Monograptus anerosus Koren, Monograptus mironovi Koren, Monograptus beatus Koren, Monograptus prognatus Koren, Monograptus bouceki Príbyl, Neocolonograptus nimius (Koren), Pseudomonoclimacis bandaletovi Mikhailova, Callograptus flabellatus Boucek, and Dictyonema cf. elongatum Boucek. All are recorded in China for the first time. The fauna, which is indistinguishable from that of the Balkhash area of Kazakhstan, shows strong endemicity, indicating that the two areas formed a single paleobiogeographic unit during the Pridoli.
A new archosaur from the Upper Triassic Pardonet Formation of British Columbia
Authors: Nicholls Elizabeth L , Brinkman Donald B , Wu Xiao-Chun
Published: April 2011

Sikannisuchus huskyi, a new genus and species of archosaur, is described from the Upper Triassic (Norian) Pardonet Formation of northeastern British Columbia. It has a broad, flat skull, and may have reached 4 m in length. It is referred to the Archosauria on the basis of a lateral mandibular fenestra, laterally compressed serrated teeth, elongate transverse processes, neural spine table, osteoderms, and thecodont dentition. It is autapomorphic in that the postfrontal enters the border of both the orbit and the supratemporal fenestra, and it has a large prefrontal that contacts both the nasal and the postfrontal, excluding the frontal from the margin of the orbit. The presence of osteoderms and a well-developed clavicle exclude Sikannisuchus from the Ornithodira; however, in the absence of any preserved limb material, we cannot assign it to the Crurotarsi. Sikannisuchus is not currently referable to any known taxon of archosaur and is left as Archosauria incertae sedis.
Geophysical studies of the structure of the Appalachian orogen in the Atlantic borderlands of Canada
Authors: Hall Jeremy , Marillier François , Dehler Sonya
Published: April 2011

Results of 6000 km of crustal seismic profiling are presented with gravity and aeromagnetic maps for the Appalachian orogen in eastern Canada. Wide-angle seismic surveys show that the central mobile belt of the orogen has a thinner crust than its margins. High-velocity lower crust, attributed to underplating, is found below the former Laurentian continental margin in Newfoundland and below the Magdalen basin. Potential field data are used to trace the surface zones of the orogen from the northeast Newfoundland shelf to Cape Breton, but extrapolation to New Brunswick and Quebec is unclear because of late Paleozoic basin development. The central mobile belt of the orogen is only a few tens of kilometres wide in southwest Newfoundland and Cape Breton, but broadens substantially to around 200 km elsewhere. Reflection images show a strong deep-crustal fabric that runs along the orogen, with a margin that crosses into the Avalon zone in southern Newfoundland but coincides with the Avalon-Gander zone boundary elsewhere. The fabric formed during mid-Silurian continental collision and (or) during postorogenic collapse. Variation in fabric pattern and metamorphic grade, tightening of structures towards southwest Newfoundland and Cape Breton, and voluminous plutonism in southern Newfoundland are all in accord with maximal crustal thickening followed by erosion and isostatic readjustment in southwest Newfoundland and Cape Breton, and relatively little in northeast Newfoundland and its adjacent shelf. Reflection fabrics in the upper crust appear to be detached from those in the deeper crust; this is attributed to rheological contrast across the base of a quartz-rich upper crust.
Large-scale liquefaction and fluidization in the Cap Chat Mélange, Quebec Appalachians
Authors: Cousineau Pierre A
Published: April 2011

The Cap Chat Mélange crops out discontinuously for 200 km along the south shore of the St. Lawrence River in the Gaspé Peninsula. It is located just south of Logan's line, the northern limit of the Humber zone with the Taconian foreland basin. This mélange is composed of dismembered rocks of the adjacent formations, in particular the Lower Ordovician Rivière Ouelle and Middle Ordovician Tourelle formations, with lesser contributions by the Middle Ordovician Des Landes and the Cambrian Orignal formations. Blocks in the mélange vary in size from a few centimetres to several kilometres, with well-preserved internal stratigraphy in the larger blocks. The distribution of blocks is not uniform and the composition of the surrounding matrix changes with corresponding changes in block composition. Tectonic processes, mostly extensional and compressional faulting, are responsible for some of the chaotic aspects of the mélange. However, the main mechanism was as follows: (i) large-scale liquefaction of the mudstone-rich Rivière Ouelle Formation, (ii) sinking with consequent dismembering of the Tourelle Formation into this underlying weakened Rivière Ouelle Formation, and (iii) fluidization of the lowermost sand beds of the Tourelle Formation resulting in abundant sandstone sills and dikes in the Rivière Ouelle Formation.
Perennial spring occurrence in the Expedition Fiord area of western Axel Heiberg Island, Canadian High Arctic
Authors: Pollard Wayne , Omelon Chris , Andersen Dale , McKay Chris
Published: April 2011

This paper documents perennial spring activity at Expedition Fiord on western Axel Heiberg Island in the Canadian High Arctic. Two groups of mineralized springs occur near the McGill University Axel Heiberg Research Station located at 79°26'N, 90°46'W. The first is at Gypsum Hill, 3 km from the terminus of the White and Thompson glaciers, and the second site is at Colour Peak, approximately 10 km downvalley near the head of Expedition Fiord. Each spring group consists of 20-40 vents spread over several hundred square metres. The highly mineralized nature of the discharge causes a freezing-point depression of 7-10°C and produces a range of precipitates and travertine deposits. Year-round water temperature and discharge rate measurements have been obtained, demonstrating perennial activity at these sites. Results indicate that temperatures range from -4.0 to 6.6°C among the individual sources; however, water temperatures at the various outlets remain constant throughout the year despite a mean annual air temperature of -15°C. Although discharge from any one outlet is low (<0.5 to 2.0 L/s), the total discharge is substantial, each year producing several seasonal frost mounds and an icing 180 000 - 300 000 m2 at the Gypsum Hill site.
δ13C stratigraphy of the Proterozoic Bylot Supergroup, Baffin Island, Canada: implications for regional lithostratigraphic correlations
Authors: Kah Linda C , Sherman Anne G , Narbonne Guy M , Knoll Andrew H , Kaufman Alan J
Published: April 2011

The Bylot Supergroup, northern Baffin Island, contains >1500 m of platform, shelf, and slope carbonates deposited between ~ 1270 and ~ 723 Ma. Limited chronostratigraphic data have led to the broad correlation of the Bylot Supergroup with predominantly Neoproterozoic successions in northern and western Laurentia; yet, detailed correlation has been impossible given biostratigraphic and lithostratigraphic limitations. Carbon-isotope chemostratigraphy represents a potential dataset to constrain such interregional correlations. Carbon isotopic data from the Bylot Supergroup and broadly coeval successions from Somerset Island and northwest Greenland reveal distinct stratigraphic trends in δ13C, with intervals of moderate 13C enrichment (+3.5 ± 1) punctuated by excursions to slightly negative values (-1.0 ± 1). Although the scale of the observed variation is muted relative to Neoproterozoic standards, the dissimilarity of values to those recorded in northwestern Laurentia suggests that these strata delineate a discrete depositional interval. Comparison of isotopic values with published data indicates that δ13C values between approximately -1.0 and +4.0 are characteristic of the interval between ~ 1300 and ~ 800 Ma. This pattern is distinct from that of younger Neoproterozoic successions, which typically record values >+5, and older Mesoproterozoic successions, which record values near 0, and suggests that these moderately positive values may be useful for broad time correlation. Compilation of new and published data permits the tentative reconstruction of a global Mesoproterozoic carbon isotopic curve.
Seismic facies and regional architecture of the Oak Ridges Moraine area, southern Ontario
Authors: Pugin A , Pullan S E , Sharpe D R
Published: April 2011

Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glacial deposits in and beneath the Oak Ridges Moraine (ORM). The focus of this paper is the role of seismic reflection surveys, and the derived seismic facies and facies geometry, in the development of a well-constrained, regional, conceptual model of the subsurface stratigraphy in the area and the improved inferences these data allow regarding glacial event sequence and process interpretations. The data define four major seismic facies that characterize the complex glacial sequence of the ORM area. High-reflectivity facies (I) can be traced regionally and related to an eroded Newmarket Till surface. Medium (II) and low (III) reflectivity facies are generally associated with coarse-grained glaciofluvial deposits and laterally extensive, glaciolacustrine sequences of sand, silt, and clay, respectively. A chaotic facies (IV) is common within buried channels, and attributed to instability and (or) rapid channel-fill deposition. Seismic geometry (with borehole verification) shows that a broad surface network of channels extends below thick ORM sediments. The channel system is part of a regional unconformity formed on the Newmarket Till (facies I). The buried channels can have steep sides, and their fills frequently include tabular sheets, eskers, and (or) large cross-beds. The observations are consistent with the scenario of sheet flow and channel cutting by high-energy subglacial meltwater and filling with gravel, sand, and silt in succession (facies II and III) as the flows waned.
Growth and demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada
Authors: Kusky Timothy M , Hudleston Peter J
Published: April 2011

The Steep Rock Group of northwest Ontario's Wabigoon subprovince is one of the world's thickest Archean carbonate platform successions. It was deposited unconformably over a 3001-2928 Ma gneissic terrane, and contains a remarkable group of biogenic and oolitic limestones, dolostones, micrites, and karst breccias capped by a thick paleosol developed between and over karst towers. The presence of aragonite fans, herringbone calcite, and rare gypsum molds suggests that the carbonate platform experienced at least local anaerobic and hypersaline depositional conditions. This sequence shows that a combination of chemical and biological processes was able to build a carbonate platform 500 m thick by 3 billion years ago. The carbonate platform is structurally overlain by a mixture of complexly deformed rocks of the Dismal Ashrock forming a mélange with blocks of ultramafic volcaniclastic rocks, mafic volcanics, carbonate, tonalite, lenses of Fe-ore rock, and metasedimentary rocks, in a shaly, serpentinitic, and fragmental ultramafic volcaniclastic matrix. The mélange shows evidence of polyphase deformation, with early high-strain fabrics formed at amphibolite facies, and later superimposed brittle fabrics related to the final emplacement of the mélange over the carbonate platform. An amphibolite- through greenschist-grade shear zone marks the upper contact of the mélange with overlying mafic volcanic and tuffaceous rocks of the ca. 2932 Ma Witch Bay allochthon, interpreted as a primitive island arc sequence. We suggest an evolutionary model for the area that begins with rifting of an arc sequence (Marmion Complex of the Wabigoon arc) that initiated subsidence and sedimentation on the Steep Rock platform and its correlatives that extend for a restored strike length exceeding 1000 km. Shallow water carbonate sedimentation continued until the platform was uplifted on the flanks of a flexural bulge related to the approach of the Witch Bay allochthon, representing collision of the rifted arc margin of the Wabigoon subprovince with the Witch Bay arc. Mélange of the Dismal Ashrock was formed as off-axis volcanic rocks were accreted to the base of the Witch Bay allochthon prior to its collision with the Steep Rock platform.
Mid-Atlantic Ridge hydrothermal events recorded by deep-sea corals
Authors: Smith Jodie E , Brand Uwe , Risk Michael J , Schwarcz Henry P
Published: April 2011

Trace-element and stable-isotope analyses were performed on azooxanthellate corals from the North Atlantic, at two different tectonic settings. One set was from Orphan Knoll, near Newfoundland (1700 m depth, 50°25.57'N, 46°22.05'W), the other from the Mid-Atlantic Ridge (1200 m depth, 45°14.12'N, 28°34.12'W). The Mid-Atlantic Ridge corals contain significantly greater quantities of Fe, Mn, Cu, Ni, and Zn within their skeletons than the Orphan Knoll corals. The metal concentrations are not homogeneous within the Mid-Atlantic Ridge coral skeletons, but occur as episodic pulses during a decade or two of each coral's lifetime. We believe these metals originated in a hydrothermal discharge zone associated with the Mid-Atlantic spreading centre. If so, it is evidence that the duration of an individual hydrothermal event is from a decade up to 30 years or so. With more specimens of known ages, it may be possible to reconstruct the history of a particular segment of an oceanic spreading centre.
Age and tectonic implications of Paleoproterozoic granitoid intrusions within the Nain Province near Nain, Labrador
Authors: Connelly James N , Ryan A Bruce
Published: April 2011

U-Pb (zircon) age determinations from three granitoid intrusions in the Nain region, formerly assigned to the well-known 1.35-1.29 Ga (Mesoproterozoic) Nain Plutonic Suite (NPS), indicate that they were emplaced, instead, during the Paleoproterozoic. Crystallization ages of 2109 ± 3 Ma for Sheet Hill granite, 2052 ± 4 Ma for Loon Island granite, and 2025 ± 7 Ma for Satok Island monzonite demonstrate a decreasing time of emplacement from north to south. Leucocratic basic rocks, superficially similar to those of the NPS, occur as inclusions within the Satok Island monzonite and are intruded by an 1873 ± 4 Ma granitic aplite dyke north of Webb's Bay. The ages clearly demonstrate granitic magmatism in the Nain area for at least 750 Ma, and anorthositic magmatism for at least 675 Ma, before the development of NPS. The earliest Paleoproterozoic magmatism (2109-2025 Ma) may have coincided with breakup of the North Atlantic craton, whereas the local magmatism represented by the 1873 Ma aplite dyke may be related to the embryonic stages of the continental collision that produced the 1860-1740 Ma Torngat Orogen. Leucocratic basic rocks associated with the Paleoproterozoic granitic rocks identified here could be Archean in age, but are more likely coeval with the granites. Other granitic and basic rocks in the Nain area may likewise be products of this bimodal plutonism. Identification of this possible geological duality suggests repetitive magmatism of "anorogenic type" over a significant time span in this part of Labrador. If the mantle-plume-related genesis accorded the Mesoproterozoic NPS is applicable to the Paleoproterozoic rocks, it implies multiple periods of similar lithosphere-asthenosphere interaction in this area, beginning at least in the Paleoproterozoic. The Paleoproterozoic magmas may have been emplaced into Nain Province crust along a linear intracontinental extension zone inboard from a rifted margin.
The Central Slave Basement Complex, Part II: age and tectonic significance of high-strain zones along the basement-cover contact
Authors: Bleeker Wouter , Ketchum John WF , Davis W J
Published: April 2011

The basement-cover high-strain zone enveloping parts of the Sleepy Dragon Complex, northeast of Yellowknife, Slave Province, Canada, has been reinvestigated. Integrated stratigraphic, structural, and geochronological data show that the high-strain zone is of regional extent and is best interpreted as a décollement between crystalline, ca. 2.9-3.3 Ga rocks of the Central Slave Basement Complex and pre-2687 Ma cover rocks. Three temporally distinct mafic dyke swarms occur within the high-strain zone. The two oldest of these constrain the timing of the high-strain event to between 2734 ± 2 and 2687 ± 1 Ma. At the time of décollement development, the cover stratigraphy consisted of (i) the Central Slave Cover Group, a thin, pre-2734 Ma succession of mafic and ultramafic volcanic rocks, conglomerates, fuchsitic quartzites, minor rhyolites, and banded iron formation; and (ii) an overlying sequence of tholeiitic pillow basalts. The Central Slave Cover Group is considered to be autochthonous, whereas a variety of evidence suggests that the pillow basalts are parautochthonous to possibly allochthonous. The transport direction in the décollement was from northeast to southwest, and maximum displacement was probably on the order of 10 to several tens of kilometres. Presently, the décollement appears discontinuous due to younger intrusive and erosional events. Around most of the southern flanks of the Sleepy Dragon Complex, the crystalline core of the complex consists of post-décollement intrusive rocks and (or) is unconformably overlain by parts of the Yellowknife Supergroup that are younger than 2687 Ma. Lineation patterns in these younger rocks reflect regional deformation events that postdate and are unrelated to the décollement. The new data allow two tectonic models for development of the décollement: (i) a contractional thrusting model, involving collision of an eastern Slave Province arc terrane; or (ii) a syn-greenstone belt extensional model.
Precise zircon geochronology in the Adirondack Lowlands and implications for revising plate-tectonic models of the Central Metasedimentary Belt and Adirondack Mountains, Grenville Province, Ontario and New York
Authors: Wasteneys Hardolph , McLelland James , Lumbers Sydney
Published: April 2011

New high-precision, single-grain dating of leucogranites from the Adirondack Lowlands, dated previously by multigrain zircon methods at ca. 1416 Ma (Wellesley Island) and ca. 1285-1230 Ma (Hyde School Gneiss), has yielded U-Pb zircon ages of ca. 1172 Ma, identical to that of Rockport granite of the Frontenac terrane. In addition, sensitive high resolution ion microprobe (SHRIMP) zircon dating of the intrusive Antwerp-Rossie suite in the Adirondack Lowlands indicates a maximum emplacement age of ca. 1207+26-11 Ma which fixes a minimum age for deposition of regional metasedimentary rocks that it crosscuts. These results remove apparent chronological discrepancies across the St. Lawrence River, thus expanding the significance of the Rockport granite and Hyde School Gneiss and requiring modification of plate-tectonic models for the Central Metasedimentary Belt and Adirondack Mountains in the interval ca. 1350-1125 Ma.
Structural and geochronological constraints on the role of partial melting during the formation of the Shuswap metamorphic core complex at the latitude of the Thor-Odin dome, British Columbia
Authors: Vanderhaeghe Olivier , Teyssier Christian , Wysoczanski Richard
Published: April 2011

At the latitude of the Thor-Odin dome, the Shuswap metamorphic core complex exposes a ~15 km thick structural section composed of an upper unit that preserved Mesozoic metamorphism, structures, and cooling ages, separated from the underlying high-grade rocks by low-angle detachment zones. Below the detachments, the core of the complex consists of an amphibolite-facies middle unit overlying a migmatitic lower unit exposed in the core of the Thor-Odin dome. Combined structural and super high resolution ion microprobe (SHRIMP) U-Pb geochronology studies indicate that the pervasive shallowly dipping foliation and east-west lineation developed in the presence of melt during Paleocene time. SHRIMP analyses of complexly zoned zircon grains suggest that the migmatites of the lower unit crystallized at ~56 Ma, and a syntectonic leucogranite at ~60 Ma. We suggest that leucogranite migrated upward from the migmatites through an array of dikes and sills that permeated the middle unit and ponded to form laccoliths spatially related to the detachment zones. The similarity in ages of inherited zircon cores in the two migmatite and the leucogranite samples suggests a genetic link consistent with the structural analysis. Following the crystallization of migmatites, the terrane cooled rapidly, as indicated by argon thermochronology. We propose that exhumation of the core of the Canadian Cordillera during the formation of the Shuswap metamorphic core complex occurred from ~60 to 56 Ma at a time when the crust was significantly partially molten. These structural and temporal relationships suggest a genetic link between mechanical weakening of the crust by partial melting, late-orogenic collapse, and exhumation of high-grade rocks in the hinterland of a thermally mature orogenic belt.
Form, facies, and depositional history of the North Long John rock avalanche, Owens Valley, California
Authors: Blair Terence C
Published: April 2011

The prehistoric but geomorphically pristine North Long John rock avalanche of the Inyo Mountains piedmont, California, formed by the catastrophic collapse and disintegration of a 500 × 1000 m range-front bedrock slab. This failure rapidly produced and transferred ~25 million cubic metres of new sediment to the piedmont, where it was deposited in a trough between two coalesced alluvial fans. The avalanche consists of nearly monolithologic (aplitic), unstratified, very angular, muddy, cobble, pebble gravel with boulders concentrated at the top and outer margins. The deposits are clast supported except in the lower central zone. Coarse clasts exhibit crackle-breccia fabric, and the voluminous equant pebbles are the disaggregated products of these clasts. The avalanche deposits are distributed in a U-shaped body with paired lateral levees 10-60 m high that extend 1560 m from the range front to a 108 m high distal snout. Each levee contains three segments that, along with the snout, overlap and extend progressively farther downslope from the inside of each other in a telescoped pattern. The most proximal deposits are the remnant sole sheared off where the avalanche intersected the piedmont, whereas the remainder was deposited as an ensuing grain flow. The radial alignment of the long axes of coarse clasts in the upper levees indicate that particle-particle interaction took place during flowage, and that clasts were pushed towards the margins. Part of the northern second levee borders a sharp and vertical, 10-18 m high scarp cleanly sliced through older fan deposits. This scarp was cut by the leading edge of the avalanche, which rapidly bulldozed away ~0.5 million cubic metres of fan deposits in the flow path. A southward cross-tilt resulted from the avalanche turning south due to interference with higher fan deposits on the north side. Friction from this interference restricted avalanche runout to 1.6 km, 25-33% of the distance predicted by empirical data from case studies lacking flow-path obstructions.
Blackriveran carbonates from the subsurface of the Lake Simcoe area, southern Ontario: stratigraphy and sedimentology of a low-energy carbonate ramp
Authors: Grimwood Jonathan L , Coniglio Mario , Armstrong Derek K
Published: April 2011

The lowest Upper Ordovician (Blackriveran) strata in the Lake Simcoe area represent the base of a major transgressive sequence of peritidal carbonates and siliciclastics. From detailed petrographic study of 12 cores that penetrate, in ascending order, the Shadow Lake, Gull River, and lower Bobcaygeon formations, seven distinctive lithofacies are recognized: (1) sandstone, siltstone, and shale; (2) dolostone and calcareous dolostone; (3) lime mudstone; (4) peloidal bioclastic wackestone and packstone; (5) peloidal bioclastic grainstone; (6) ooid grainstone; and (7) intraclastic bioclastic wackestone and packstone. Metre-scale cycles, like those reported from numerous other peritidal deposits, are apparently absent in this succession. In addition, these strata are commonly interrupted by a variety of hardgrounds. The carbonate strata can be grouped into four lithofacies associations that represent deposition in generally low energy, tropical paleoenvironments along a southward-facing, homoclinal ramp that was frequently influenced by storms. Rapid facies changes along depositional strike likely resulted from a combination of an irregular basement topography and coastline geometry. The coexistence of Heterozoan and Photozoan carbonates in the lower Bobcaygeon Formation probably reflects the increasing incorporation of cooler oceanic waters as the ramp gradually deepened during the Tippecanoe transgression rather than the onset of more temperate climatic conditions.
Cosmogenic 36Cl dating of the maximum limit of the Laurentide Ice Sheet in southwestern Alberta
Authors: Jackson, Jr. Lionel E , Phillips Fred M , Little Edward C
Published: April 2011

Cosmogenic 36Cl ages were determined on 11 glacial erratics from the summits of Porcupine Hills and Cloudy Ridge, Waterton valley, and the Foothills south of Cardston, Alberta. These erratics were derived from the Canadian Shield and the Rocky Mountains of the Waterton area. They were laid down by (1) the most extensive advance of a Canadian Shield centred continental ice sheet into this region (stratigraphically oldest glacial deposits); (2) a montane glacial advance from the Waterton valley (stratigraphically intermediate glacial deposits); and (3) an advance of continental glacial ice that overrode deposits of the intermediate-age montane advance. Zero erosion rate 36Cl ages of the erratics, uncorrected for snow cover, range between about 12 and 18 ka. They support the hypothesis that the Laurentide Ice Sheet reached farther into the southwestern Foothills than did all the previous continental ice sheets.
Crustal formation in the Grenville Province: Nd-isotope evidence
Authors: Dickin A P
Published: April 2011

Ninety-eight new Nd-isotope analyses are presented for gneissic rocks from the Grenville Province. When combined with over 250 published Nd analyses and some unpublished analyses, these data can be used to establish a first-order crustal formation age map for most of the Grenville parautochthon and allochthonous polycyclic belt. In particular, the geographic extents of a juvenile Labradorian arc (Labradoria) and a juvenile 1.5 Ga arc (Quebecia) are defined, each with an area probably in excess of 100 000 km2. In addition, pre-1.75 Ga arcs are identified in Ontario (Barilia) and Labrador (Makkovikia). This work largely fills the last major gap in the continent-wide crustal formation age map of the Precambrian Shield of North America.
Melt-related metasomatism in mafic granulites of the Quetico subprovince, Ontario: constraints from O-Sr-Nd isotopic and fluid inclusion data
Authors: Pan Y , Fleet M E , Longstaffe F J
Published: April 2011

Mafic granulites in the Archean Quetico subprovince, north of Manitouwadge, Ontario, occur as isolated lenses or discontinuous layers in spatial association with tonalitic leucosomes in metasedimentary rocks and exhibit concentric zoning from a biotite-rich margin to an orthopyroxene-rich outer zone and a clinopyroxene-rich central zone, with internal orthopyroxene-bearing leucosomes and, rarely, patches of relict amphibolites within the clinopyroxene-rich zone. Microstructural and microchemical evidence suggests that the mafic granulites formed from amphibolites by combined infiltration-diffusion processes in the presence of a P-F-bearing silicate melt ((P2O5)melt = 0.24-0.28 wt.%) and a CO2-rich (hypersaline?) fluid. The whole-rock and mineral δ18O values of the mafic granulites (8-9 V-SMOW) indicate oxygen-isotope equilibration between amphibolites (6.6-6.9) and associated tonalitic leucosomes (9.5-10) at 700-800°C. Strontium- and Nd-isotope data and U-Pb zircon ages confirm isotopic homogenization at the leucosome-amphibolite boundaries during the peak granulite-facies metamorphism at about 2650 Ma. Texturally, early CO2-rich fluid inclusions in quartz and garnet yield P-T conditions similar to those of the peak granulite-facies metamorphism. Hypersaline fluid inclusions occur in textural coexistence with the early CO2-rich inclusions, but are invariably low in homogenization temperatures (178-234°C). This study shows that silicate melts not only provide a conduit for CO2-rich fluids but also interact directly with country rocks for the formation of granulites. Also, the O-Sr-Nd isotope data show that the documented mobility of rare-earth elements in the Quetico granulite zone is localized in scale and related to anatexis of local metasedimentary rocks during the granulite-facies metamorphism.
Comportement du système U-Pb dans la monazite et chronologie de la déformation et du métamorphisme des metasédiments du domaine de Kisseynew, orogène trans-hudsonien (Manitoba, Canada)
Authors: Parent Martin , Machado Nuno , Zwanzig Herman
Published: April 2011

The Kisseynew domain is the central unit of the Reindeer Zone of the Paleoproterozoic Trans-Hudson Orogen, in Manitoba and Saskatchewan. The southern flank of the domain is a transition zone between the greenschist facies of the volcano-plutonic assemblage of the Flin Flon - Snow Lake belt and the upper amphibolite facies of Kisseynew paragneisses. The Jungle Lake area, in the southern flank of the Kisseynew Domain, comprises mainly quartzofeldspathic gneisses representing continental clastic units of the Missi suite and migmatitic metagraywackes of the Burntwood suite. The area was affected by several phases of deformation, metamorphism, and migmatisation. Detailed mapping and U-Pb geochronology were carried out in order to establish the timing of the deformational and metamorphic phases. The oldest leucosome contains sillimanite formed during peak metamorphism and is associated with F2 folding and S2 fabric. Five single monazites from this leucosome yield ages between 1809 and 1803 Ma taken as the best estimate for the duration of peak metamorphism. Biotite schlieren in diatexites in the Burntwood suite show a S2 fabric folded by F3. Zircon from one of these diatexites yield a crystallization age of 1798+3-2 Ma, considered as the lower limit for the F2 event. Single monazites from the same rock yield ages between 1812 and 1789 Ma, the oldest of which are considered to be inherited. The youngest mobilisate is a pegmatite crosscutting F2 and F3 fabrics and yielded single monazite ages between 1875 and 1788 Ma. The youngest age is taken as the age of the pegmatite and is a minimum age for F3 fabrics. These results, together with those from other areas of the southern Kisseynew Domain, indicate a ca. 30 million year period (1818 and 1785 Ma) of continuous deformation and metamorphism. The data also show the presence of monazite crystals of different ages in the same rock illustrating the need to analyse single grains to obtain geologically meaningful ages.
Geochemistry of the Cretaceous-Tertiary (K-T) boundary interval: south-central Saskatchewan and Montana
Authors: Lerbekmo J F , Sweet A R , Davidson R A
Published: April 2011

The Cretaceous-Tertiary (K-T) boundary interval in the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project Wood Mountain and Wood Mountain Creek core holes along with the Wood Mountain Creek and Rock Creek east A outcrop localities, south-central Saskatchewan, were analyzed using either neutron activation analysis or laser ablation - inductively coupled plasma - mass spectrometry. The claystone towards the base of the Landscape coal zone in the Wood Mountain core hole which coincides with a floristic extinction event was found to have enhanced iridium values, confirming it to be the boundary claystone. Four layers, sub-hackly, hackly, satiny, and laminated, in ascending stratigraphic order, recognizable as part of the boundary claystone in south-central Saskatchewan, are considered to be correlative to previously documented layering in midcontinental United States. Present results indicate both a uniqueness and possible common genesis of these layers. The hackly and satiny claystones have relatively low iridium abundances in comparison to the laminated shale. This pattern is regional in extent and therefore the geochemistry of these layers is accepted as a primary characteristic. Anomalous iridium abundances occur beyond the boundary claystone interval, requiring an explanation more complex than post-depositional chemical migration. As a generalization, the Cyathidites spore spike first occurs in the satiny claystone.
Sudbury-type breccias in the Huronian Gowganda Formation near Whitefish Falls, Ontario: products of diabase intrusion into incompletely consolidated sediments?
Authors: Shaw CSJ , Young G M , Fedo C M
Published: April 2011

Sudbury breccias are commonly attributed to meteoritic impact at about 1.85 Ga in the vicinity of the Sudbury Igneous Complex. In the Whitefish Falls area, about 75 km southwest of Sudbury, similar breccias are widely developed in argillites of the ~2.3 Ga Gowganda Formation. There is abundant evidence of "soft sediment" deformation of the Huronian sediments in the form of complex "fault" contacts, clastic dyke intrusions, and chaotic folding. These movements appear to have been penecontemporaneous with intrusion of highly irregular diabase bodies, which are interpreted as being older than the ~2.2 Ga Nipissing diabase. Complex shapes of diabase bodies and highly irregular contact relationships between diabase and argillites, including intrusions of sediment veins into diabase, support intrusion of the diabase into incompletely consolidated sediments. These data, together with chemical evidence of mixing of diabase, argillite, and other materials in the breccia bodies, suggest that the breccias at Whitefish Falls may have formed as a result of interaction between hot mafic magma and semiconsolidated, water-rich mud, more than 350 Ma prior to formation of the Sudbury Igneous Complex and attendant phenomena that are presumed to be impact related.
Tectono-thermal evolution of deep crust in a Mesoproterozoic continental collision setting: the Manicouagan example
Authors: Indares Aphrodite , Dunning Greg , Cox Richard
Published: April 2011

High-pressure metamorphic rocks in continental collision belts provide important information on the orogenic evolution of deep crust. In the Grenville Province, a prime example is the Manicouagan Imbricate Zone (MIZ), a Mesoproterozoic crustal section that was metamorphosed up to 1800 MPa and 850-950°C at ~1050 Ma. High temperatures and the presence of synmetamorphic within-plate tholeiitic gabbro intrusion in the MIZ attest to thermal perturbation during burial and emplacement of mantle-derived melts, consistent with thinning of lithospheric mantle. Subsequently, the MIZ was extruded by a combination of northwest-directed thrusting over a crustal-scale ramp and extension at higher crustal levels. In the middle MIZ, extension was coeval with thrusting, but perpendicular to the thrust direction, and was apparently controlled by ductility contrasts between slices. In contrast, the highest levels show evidence of southeast-directed extension, i.e., of opposite sense to the thrust direction, that postdated thrusting within the MIZ. This episode was followed by renewed northwest-directed thrusting of medium-pressure Mesoproterozoic units over the MIZ, and then by final southeast-directed extension. Overall configuration of the MIZ was achieved between ~1040-990 Ma and is consistent with outward propagation of the orogen. Alternating periods of thrusting and extension displacement are a likely result of adjustments permitting maintenance of dynamic equilibrium within the advancing stack. The tectonothermal characteristics of the MIZ allow comparison between the Grenville Province and younger, thermally perturbed orogens (i.e., Variscan Belt) and may be the final product of a Tibetan Plateau style evolution.
Geologic transect across the Grenville orogen of Ontario and New York
Authors: Carr S D , Easton R M , Jamieson R A , Culshaw N G
Published: April 2011

Revised cross sections of the western Grenville Province incorporate new geologic results and reprocessed seismic reflection data. The geology is presented in terms of three tectonic elements: (1) "pre-Grenvillian Laurentia and its margin" with ca. 1740 and 1450 Ma continental arc plutons and associated supracrustal rocks; (2) "Composite Arc Belt" of allochthonous ~1300-1250 Ma volcanic arcs and sedimentary rocks; and (3) "Frontenac-Adirondack Belt" characterized by supracrustal and granitoid rocks, and anorthosites, of uncertain affinity, that may represent a distinctive part of the Composite Arc Belt or an offshore (micro)continent. Rocks of the Composite Arc and Frontenac-Adirondack belts were amalgamated with each other by ca. 1160 Ma, were then thrust over Laurentia during ca. 1080-1035 Ma and ca. 1010-980 Ma phases of convergence, and were dissected and exhumed by <1040 Ma normal faults. Penetrative deformation was restricted to that part of the pre-Grenvillian Laurentian margin that lies to the southeast of the Grenville front and parts of the accreted Composite Arc and Frontenac-Adirondack belts. The Laurentian rocks in the Grenville Province are bounded to the northwest and southeast by southeast-dipping ductile thrust and (or) normal shear zones. The Composite Arc and Frontenac-Adirondack belts to the southeast are bounded by ductile and brittle-ductile thrust and (or) normal faults that separate domains with contrasting cooling histories. Despite a long pre-Grenvillian tectonic and plutonic history, the present crustal architecture and much of the seismic reflectivity were acquired during 1080-980 Ma phases of compression and extension.