bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology of the Hammer Down mesothermal gold deposit, Newfoundland Appalachians, Canada
Authors: Gaboury Damien , Dubé Benoît , Laflèche Marc R. , Lauzière Kathleen
Published: April 2011

The Hammer Down gold deposit is one of the most significant mesothermal vein-type gold deposits in the Canadian Appalachians. It is located within a complex sequence of Ordovician, mafic-dominated tholeiitic and calc-alkalic and arc-related volcanic rocks, which was intruded by Silurian felsic porphyry dykes. The host rocks have undergone complex polyphase deformation. At least three deformational events influenced vein emplacement and overall geometry of the deposit. A Taconian deformation (D1–2) was responsible for the development of a 250 m wide zone of high-strain deformation (HSZ1) at the interface between two blocks of Ordovician rocks: the Catcher's Pond Group and the Lush's Bight Group. Rocks included within the HSZ1, represent "exotic" slabs of volcanic rocks that were tectonically juxtaposed, intensively foliated (S1), and folded (F2). Gold occurs in high-grade, sulfide-rich, fault-fill quartz veins that occur within the HSZ1. At the outcrop scale, these veins are hosted by discrete centimetre- to metre-wide ductile–brittle D3 high-strain zones (HSZ3) of Silurian or younger age. The development of the gold-hosting structures (HSZ3) is genetically related to layer anisotropy induced by intrafolial F2 folds, and most importantly by the presence of felsic porphyry dykes, which were competent compared to the intensively foliated and incompetent mafic volcanic rock sequence. A postmineralization D4–5 deformation, which included two generations of folds (F4 and F5) and late brittle faulting, is responsible for the actual geometry of the deposit.
Ice-flow history and glacial dispersal patterns, southeastern Cape Breton Island, Nova Scotia: implications for mineral exploration
Authors: McClenaghan M. B. , DiLabio R. N. W.
Published: April 2011

Regional till sampling and stratigraphic studies were completed in southeastern Cape Breton Island, Nova Scotia, in 1990 and 1991 to document the directions and distances that successive ice-flow events have dispersed material and to document regional till geochemical patterns to aid mineral exploration in this heavily drift-covered area. Three major Wisconsinan ice-flow events affected the area: an early eastward flow, followed by a northeastward flow, and finally a southward flow. The shape and magnitude of dispersal trains in the area are the net result of the three ice-flow events, which are variable from north to south. In the north, the northeast ice flow was the dominant erosive and depositional event, producing a large northeast-trending drumlin field. Salmon River porphyry clasts and Pb- and Zn-rich till from the Yava Pb mine were dispersed more than 15 km to the northeast. In the south, eastward ice flow was the dominant erosive and depositional event, producing large east-trending till ridges. Dispersal in this area is difficult to detect because exotic red silty till in the giant till ridges masks underlying mineralized bedrock and dilutes the locally derived glacial debris. Many precious and base metal anomalies and dispersal trains were identified in the regional till samples, several of which are related to unknown mineralized sources.
Wenlock–Ludlow graptolite biostratigraphy and extinction: a reassessment from the southwestern Iberian Peninsula (Spain and Portugal)
Authors: Gutiérrez-Marco J. C. , Lenz A. C. , Robardet M. , Piçarra J. M.
Published: April 2011

A detailed reexamination of a key Wenlock–Ludlow transition section in the Valle syncline region, Spain, and the incorportation of data from a coeval section in the Barrancos area, Portugal, both within the Ossa Morena Zone, reveal seven biostratigraphic units. These are Monograptus belophorus? and Cyrtograptus lundgreni−Monograptus testis biozones, representing the upper Sheinwoodian and the preextinction, lower Homerian faunas, respectively; the Pristiograptus dubius "parvus" – Gothograptus "nassa" Concurrent Range Biozone, Colonograptus? praedeubeli – Colonograptus? deubeli Biozone, and Colonograptus? ludensis Biozone, representing the upper Homerian postextinction faunas; and the Ludlow Neodiversograptus nilssoni and Saetograptus fritschi linearis biozones. The extinction beds between the lower Homerian lundgreni−testis Biozone and the lowest upper Homerian dubius "parvus"−"nassa" Interval Biozone make up a several centimetre thick, soft, orange-weathered, almost barren, volcanic? bed.
A recently discovered amphibian trackway (Dromillopus quadrifidus) at Joggins, Nova Scotia
Authors: Mossman David J. , Grantham Robert G.
Published: April 2011

In 1990, a hypotype of the ichnospecies Dromillopus quadrifidus Matthew, 1905 was discovered preserved as a cast in a rockfall of fine-grained Pennsylvanian (Westphalian B) sandstone at Joggins, Nova Scotia. The hypotype of this tetrapod trackway, while possessing all the morphological features evident in the holotype, is about five times larger. It also exhibits relatively subtle salamandroid affinities, thus helping confirm the original assignation. Minimum length of the adult amphibian trackmaker is estimated at 20 cm.
Evidence for pyroclastic emplacement of the Crowsnest Formation, Alberta
Authors: Adair R.N. , Burwash R.A.
Published: April 2011

The middle Cretaceous Crowsnest Formation west of Coleman, Alberta, is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts. Comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows, surges, fallout of material from vertical eruption columns, and minor mud flows emplaced the deposits. Textural evidence in the form of plastically deformed volcanic fragments, chilled deposit margins, baked rock fragment margins, recrystallization, and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature. Massive deposits containing a fine-grained basal zone are interpreted as the product of pyroclastic flows, whereas deposits characterized by a block-rich base overlain by a thin layer of block-depleted stratified material are interpreted as the product of density-stratified surges. Deposits exhibiting pronounced stratification were emplaced by ash-cloud surges. Thickly bedded breccias exhibiting rheomorphic textures were emplaced as vent-proximal pyroclastic flows. Deposits characterized by parallel beds and graded structures are interpreted as fallout tephra deposits, and deposition by lahars is indicated by coarse-grained beds that lack evidence for emplacement at elevated temperatures. The eruptions of the Crowsnest Formation were cyclical. An initial explosive phase generated deposits by pyroclastic flows, surges, fallout, and lahars. As an eruption progressed, it evolved into a poorly gas-charged effusive stage that emplaced coarsely porphyritic domes, plugs, spines, and vent-proximal lava flows. Subsequent eruptions destroyed the effusive vent facies deposits and produced abundant heterolithic clasts typical of the formation.
Paleomagnetism of pre-Grenvillian mafic rocks from the northeast Grenville Province, Labrador: implications for the Grenville Track
Authors: Park John K. , Gower Charles F.
Published: April 2011

A paleomagnetic study of mafic plutonic rocks in the northeast Grenville Province found five magnetizations, interpreted as Grenvillian and later overprints. Components A, B, and C, with the highest unblocking temperatures and distinct regional distributions, have paleopoles that appear to lie on the Grenville Track. Component C, with pole at 348°E, 11°S (δp, δm = 2°, 4°) and mostly distributed in lower-grade mafic rocks in the Groswater Bay terrane near the Grenville Front, is interpreted as a post ca. 970 Ma Grenville overprint, predating components A and B. The latter components, nearly coextensive in distribution in the Groswater Bay and Sandwich Bay regions farther south, have respective poles at 326°E, 02°N (N = 9 sites; δp, δm = 8°, 11°) and 348°E, 13°N (N = 13 sites; δp, δm = 6°, 8°). Component B could be interpreted either as a Grenville overprint or, more likely, as a later overprint of late Neoproterozoic (615 Ma) to Cambrian age due to rifting in the Lake Melville region. If so, many other so-called "Grenville" overprints from rock units within or near the St. Lawrence rift system may have been erroneously attributed to Grenvillian thermal effects and, in fact, be younger. If component B is post-Grenville and component C, a Grenville overprint, then component A is probably latest Grenvillian or later Neoproterozoic in age. These results strongly suggest that the Grenville Track needs reinterpretation.
The southern limit of Cordilleran ice in the Colville and Pend Oreille valleys of northeastern Washington during the Late Wisconsin glaciation
Authors: Carrara Paul E. , Kiver Eugene P. , Stradling Dale F.
Published: April 2011

The southern limit of the lobes of the Cordilleran ice sheet in the Colville and Pend Oreille valleys of northeastern Washington during the Late Wisconsin (Fraser) glaciation has been placed at widely different positions by various investigators. The confusion that resulted in these different positions is due to the fact that both lobes, at times, terminated in glacial lakes and much of the terminal area of the Pend Oreille River lobe was swept by floods from glacial Lake Missoula. Evidence, presented in this paper, of the southern limit of these two lobes during the Late Wisconsin glaciation consists of (i) the southern limit of Late Wisconsinan till, (ii) the southern limit of lateral meltwater channels, (iii) meltwater channels whose headward areas coincide with the southern limit of Late Wisconsinan till, and (iv) reconstructed ice-surface profiles. This evidence suggests that the southern limit of the Colville lobe is represented by a moraine near the town of Springdale, whereas that of the Pend Oreille River lobe is near the town of Newport. The timing and extent of Late Wisconsinan deglaciation in the Colville Valley are provided by radiocarbon ages and Late Pleistocene tephras at sites upglacier from thfe terminal position. These data demonstrate that the Colville lobe had retreated at least 50 km by about 12 450 BP. In the Pend Oreille Valley, the presence of a Glacier Peak tephra layer near the town of lone indicates that the Pend Oreille River lobe had retreated at least 70 km prior to deposition of the tephra.
A search for shocked quartz at the Triassic-Jurassic boundary in the Fundy and Newark basins of the Newark Supergroup
Authors: Mossman David J , Grantham Robert G , Langenhorst Falko
Published: April 2011

Triassic-Jurassic rift basins associated with the breakup of Pangea preserve key geological elements of a defining interval in Earth history. In eastern North America, the Fundy basin is the largest and deepest of nine major early Mesozoic basins of the Newark Supergroup. Overall, the stratigraphic succession is that of continental sediments, primarily fluvial, eolian, and playa lacustrine facies. In the Fundy basin, the Triassic-Jurassic boundary, as palynologically defined, is located within a few metres of the base of the North Mountain Basalt. In the Jacksonwald Syncline of the Newark basin, the boundary is precisely correlated to a "fern spike" coincident with geologically rapid Late Triassic extinctions. If meteorite impact is held to account for extinctions at the Triassic-Jurassic boundary, then shocked quartz, the most important and unequivocal evidence of terrestrial impact, should be preserved in strata of the appropriate time interval. Quartz-bearing rocks below the North Mountain Basalt display in thin section up to five different sets of subparallel, subplanar features, which contain numerous tiny voids causing the optical contrast. Within error limits, universal-stage measurements reveal that the features seem to be oriented parallel to rhombohedral planes, which would favour their shock origin. Transmitted electron microscopic observations of the same grains show, however, that the optically visible features are subgrain boundaries. Many perfect dislocations present in the quartz grains clearly indicate tectonic origin. This microstructure is distinctly different from that of shocked quartz, which is free of dislocations and contains amorphous silica lamellae, the so-called planar deformation features. A catastrophic impact event at the Triassic-Jurassic boundary, however, cannot be excluded, because this boundary has not yet been comprehensively investigated.
Upper Cretaceous - lower Tertiary lithostratigraphic relationships of three cores from Alberta, Saskatchewan, and Manitoba, Canada
Authors: Braman D R , Sweet A R , Lerbekmo J F
Published: April 2011

Cores from three stratigraphic test holes provide a relatively complete section from the lower Maastrichtian into the Paleocene. The hole drilled in the Cypress Hills of Alberta recovered core from the Ravenscrag Formation to the top of the Eastend Formation and demonstrated that most of the stratigraphy above the Battle Formation is assignable to the Ravenscrag Formation. The hole drilled in the Wood Mountain area of Saskatchewan recovered core from the Ravenscrag Formation to the Bearpaw Formation. This core helps explain the difficulty that has been encountered subdividing the interval between the Bearpaw and Ravenscrag formations into separate formations and provides a cored record of all the Ravenscrag coals within the Wood Mountain area. The core hole drilled at Turtle Mountain, Manitoba, recovered core from the Turtle Mountain Formation to the Pierre Formation. It demonstrates the difficulty in separating the Peace Garden and Goodlands members of the Turtle Mountain Formation, is useful as a principal reference section for the Coulter Member of the Pierre Formation, documents a disconformity within the Pierre Formation, and crosses the obscure contact between the Coulter and Odanah members.
Paleobotanical evidence for ecosystem disruption at the Cretaceous-Tertiary boundary from Wood Mountain, Saskatchewan, Canada
Authors: McIver E E
Published: April 2011

A continuous, subsurface Cretaceous-Tertiary boundary section, including the boundary clay within an 87 cm thick lignite, has been recovered from a core hole near Wood Mountain, Saskatchewan, Canada. The lignite-encompassed clay layer with geochemical anomaly indicates that peat deposition was continuous across the boundary. Core data indicate that, locally, a pre-boundary, conifer-dominated swamp was abruptly replaced by an angiosperm-dominated, herbaceous wetland. Sudden extermination of the dominant forest elements indicates mass kill at the level of the boundary and supports the theory of extraterrestrial impact accompanied by catastrophic destruction. Devastation of the standing vegetation may have been caused by one or more of the killing agents predicted to have accompanied impact, including freezing temperatures caused by atmospheric dust, acid rain, thermal pulse, and shock waves. There is no evidence supporting wildfires as a killing agent. Vegetational change apparent within the boundary interval is consistent with observations elsewhere in the Western Interior of North America of abrupt replacement of an ecosystem. Early Paleocene reestablishment of the cypress swamp vegetation is calculated to have taken from 1 to 5 millennia.
Deformation styles at the Appalachian structural front, western Newfoundland: implications of new industry seismic reflection data
Authors: Stockmal Glen S , Slingsby Art , Waldron John WF
Published: April 2011

New seismic reflection data gathered during hydrocarbon exploration in and adjacent to the external Humber zone, western Newfoundland, have important implications for the interpretation of structural style at the Appalachian front. These new data indicate that the structural front is influenced by both thin-skinned and thick-skinned structures. Where the structural front is thin skinned, it is characterized by a triangle zone, or tectonic wedge, similar to structures observed at the southeastern margin of the Canadian Cordillera, and at other orogenic fronts. The thin-skinned tectonic wedge is overridden locally by thick-skinned thrusts, which are generally emergent but are locally blind, forming a thick-skinned tectonic wedge. Timing relationships indicate that, although initial motion occurred during the Early to Middle Ordovician Taconian orogeny, the thin-skinned allochthonous slices in western Newfoundland were not emplaced until Devonian time (the Acadian orogeny). Thick-skinned deformation, which postdates thin-skinned thrusting, probably occurred between Middle Devonian and earliest Carboniferous time.
Heinrich event-0 (DC-0) in sediment cores from the northwest Labrador Sea: recording events in Cumberland Sound?
Authors: Kirby Matthew E
Published: April 2011

Layers of ice-rafted, limestone debris rich sediment were deposited in the northwest Labrador Sea and the North Atlantic during the last glacial period (10-80 ka); these sediments were deposited by Heinrich events (H), events which record catastrophic collapses of the Laurentide Ice Sheet in the region of the Hudson Strait. These intervals of detrital carbonate rich sediments are referred to as detrital carbonate layers (DC) in the northwest Labrador Sea. Accelerator mass spectrometry (AMS) 14C dates provide a strong constraint on the timing for these events; H-1 = DC-1 and H-2 = DC-2. DC-0, also known as H-0, correlative to the Younger Dryas cooling event, is not as distinct a sediment unit in the northwest Labrador Sea as DC-1 and DC-2. An analysis of sediments from two cores (HU75009-IV-055 and HU75009-IV-056) off the mouth of the Hudson Strait in the northwest Labrador Sea basin sheds new light on the "missing" DC-0 sediment unit. Timing for the DC-0 event in cores 055 and 056 is bracketed between 11.3 ka ± 105 years and 10.4 ka ± 185 years based on AMS 14C dates. Sedimentology of the DC-0 unit reveals a sediment layer rich in ice-rafted debris with an increase in percentage of dolomite (representative material <2 mm), clay-size dolomite, and kaolinite; it is significantly different from DC-1 and DC-2 in the same analyzed cores. For example, the percent carbonate increase in DC-1 and DC-2 is approximately three to four times higher than that in DC-0. In addition, DC-1 and DC-2 show clear evidence for mass sediment transport processes which are not observed in DC-0. From these data, the DC-0 sediment unit in the northwest Labrador Sea records Cumberland Sound ice margin change and, for reasons addressed in this paper, the Hudson Strait does not play a major role in the deposition of DC-0 sediments at these core sites. Provenance indicators, such as kaolinite and dolomite, from the core study sediments corroborate this hypothesis. These results provide strong evidence for Cumberland Sound ice margin activity and sediment contribution during DC events, specifically DC-0, and additional evidence for multiple and synchronous ice margin change along the eastern Laurentide ice margin during the Late Wisconsinan, thus further supporting an atmospheric forcing mechanism for Late Wisconsinan ice sheet change.
The Middle Cambrian Burgess Shale and its relationship to the Stephen Formation in the southern Canadian Rocky Mountains
Authors: Fletcher Terence P , Collins Desmond H
Published: April 2011

The Burgess Shale has been an anomalous geologic unit ever since Walcott named it in 1911 as the geographic equivalent of the Ogygopsis Shale in the Middle Cambrian Stephen Formation of southeastern British Columbia, but it has never been recognized outside of its type locality, so its status relative to the Stephen Formation remained uncertain. The geologic setting of the Burgess Shale was determined by Aitken and Fritz in 1968, when they recognized the Cathedral Escarpment and divided the Stephen Formation into a "thin" platformal succession on top of the Escarpment, and a "thick" basinal succession, which included Walcott's Burgess Shale, in front. Fieldwork by Royal Ontario Museum parties between 1982 and 1997 has now demonstrated that the thin and thick Stephen successions lie within different facies belts and should be regarded as separate formations; the Stephen Shale Formation is part of the Middle Carbonate Belt succession, whereas the name Burgess Shale Formation is applied to the thick basinal succession within the Outer Detrital Belt Chancellor Group. Ten distinct members are recognized in the Burgess Shale: Kicking Horse Shale, Yoho River Limestone, Campsite Cliff Shale, Wash Limestone, Walcott Quarry Shale, Raymond Quarry Shale, Emerald Lake Oncolite, Odaray Shale, Paradox Limestone, and Marpole Limestone. In contrast to the Stephen Shale Formation with its nonsequences, the thicker Burgess Shale Formation seems to represent continuous deposition spanning the Glossopleura to Bathyuriscus-Elrathina zonal boundary, incorporating the Polypleuraspis insignis and Pagetia bootes subzones and the main part of the Pagetia walcotti subzone.
Will earthquake activity in eastern Canada increase in the next few thousand years?
Authors: Wu Patrick
Published: April 2011

Knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories. Assuming that fault instability portends earthquake activity, the rate of change in fault instability for the next few thousand years in eastern Canada is computed for two viscosity models. It is shown that a uniform-viscosity (1 x 1021 Pa ·s) mantle predicts decreasing fault instability. However, a high-viscosity (1 x 1023 Pa ·s) lower mantle predicts a significant increase in fault instability, with an overall rate of -0.06 MPa/ka. Due to the lack of consensus on lower mantle viscosity, the case for increasing earthquake activity is definitely a possibility, so more study on mantle rheology, ice deglaciation history, and intraplate earthquakes in the planning of nuclear waste repositories is needed.
Nd isotopic characteristics of metamorphic and plutonic rocks of the Coast Mountains near Prince Rupert, British Columbia
Authors: Patchett P J , Gehrels G E , Isachsen C E
Published: April 2011

Nd isotopic data are presented for a suite of metamorphic and plutonic rocks from a traverse across the Coast Mountains between Terrace and Prince Rupert, British Columbia, and for three contrasting batholiths in the Omineca Belt of southern Yukon. A presumed metamorphic equivalent of Jurassic volcanic rocks of the Stikine terrane gives epsilon Nd = +6, and a number of other metaigneous and metasedimentary rocks in the core of the Coast Mountains give epsilon Nd values from +3 to +7. A single metasedimentary rock approximately 3 km east of the Work Channel shear zone gives a epsilon Nd value of -9. Coast Belt plutons in the traverse yield epsilon Nd from -1 to +2. The Omineca Belt plutons give epsilon Nd from -10 to -17. All results are consistent with published data in demonstrating that (i) juvenile origins for both igneous and metamorphic rocks are common in the Coast Belt; (ii) representatives of a continental-margin sedimentary sequence with Precambrian crustal Nd are tectonically interleaved in the Coast Mountains; (iii) Coast Mountains plutons can be interpreted as derived from a blend of metamorphic rocks like those seen at the surface, or as arc-type melts contaminated with the older crustal component; and (iv) Omineca Belt plutons are dominated by remelted Precambrian crustal rocks.
The Queenston Formation: shale-dominated, mixed terrigenous-carbonate deposits of Upper Ordovician, semiarid, muddy shores in Ontario, Canada
Authors: Brogly P J , Martini I P , Middleton G V
Published: April 2011

The Upper Ordovician Queenston Formation constitutes the westernmost part of the Taconic clastic wedge of eastern North America. In Ontario, the Queenston Formation consists of a mixed terrigenous-carbonate succession composed primarily of red silty shales, which are locally gypsiferous, alternating, in the middle and lower parts of the formation, with thin grey shales, calcareous siltstone and sandstone, and bioclastic limestone. Brachiopods, some ostracodes, and, in the lower beds, bryozoans constitute the body fossil assemblage. Diplocraterion, Skolithos, Chondrites, and occasional large vertical burrows of unknown origin form the ichnofauna. Plane beds, ripple marks, and occasional swaley and hummocky cross-stratifications are present in the calcareous units. Mudcracks, gypsum nodules, occasional halite hopper casts, and gilgai-like structures typically occur in horizons where shales alternate with siltstone and limestone. These features are indicative of prograding muddy and storm- and tide-affected shores. In southernmost Ontario, the upper part of the formation is mostly composed of a red shale, with local recognizable shale-filled channels. This shale is of paralic origin, and it is truncated by the unconformity separating the Ordovician from the Silurian units in this region. This last event may, in part, be related to a eustatic sea-level drop due to the contemporaneous Saharan glaciation, if not exclusively due to tectonic movements.
Seismic reflection and borehole geophysical investigations in the Matagami mining camp
Authors: Adam Erick , Milkereit Bernd , Mareschal Marianne
Published: April 2011

A high-frequency vibroseis seismic survey was conducted by Lithoprobe across a well-known section of the Matagami mining camp to assess the usefulness of seismic methods in lithological mapping. The data have been reprocessed to enhance shallow reflections. Critical processing steps for the preservation of the shallow features include refraction static corrections, cross-dip corrections, and first break mutes. The seismic data were calibrated using geophysical logs from two boreholes adjacent to the profile. Physical rock property measurements suggest that strong reflectivity within the volcanic sequence occurs at rhyolite-gabbro contacts. The Lower Wabassee Group, a sequence of gabbros and basalts with interlayered rhyolite horizons, has been identified as a seismic marker. This reflective package overlays the horizon where most sulphide deposits are known to be located. In the Matagami mining camp, seismic reflection methods can be used to map the deep volcanic stratigraphy and structures.
Linear zones, seismicity, and the possibility of a major earthquake in the intraplate western Lake Ontario area of eastern North America
Authors: Wallach J L , Mohajer A A , Thomas R L
Published: April 2011

Seismic hazard assessments conducted in eastern Canada rely on seismological data, which are essential, but alone, inadequate. That is because the earthquake record is too short to provide a representative picture of where large earthquakes have occurred in the past. Consequently, seismic hazard may be underestimated in areas, such as that encompassing western Lake Ontario, that are devoid of documented large earthquakes. To attempt to ascertain the likelihood of a major earthquake occurring in that highly populated and industrialized area, three regionally extensive geophysically expressed lineaments were investigated and the results were combined with available seismological information. The most conspicuous is the Niagara-Pickering linear zone, within which there have been at least two, if not three, periods of brittle faulting, including displacements compatible with the current stress field. It also appears to represent the same major structure as the Akron magnetic boundary in eastern Ohio, the site of the mb = 4.9 Leroy earthquake. The second is the Georgian Bay linear zone, which extends from Georgian Bay to New York State. It displays evidence of recent outcrop-scale faulting, an alignment of earthquakes along its southwestern boundary, and a possible spatial relationship to other earthquakes, including two of M >= 5. Lastly, there is the Hamilton - Lake Erie lineament, which is parallel and proximal to a possible fault and coincides with a linear array of small to moderate earthquakes. All three converge on the western Lake Ontario area, which has a higher frequency of seismicity than the adjacent areas. Thus, the western Lake Ontario area might have a greater potential to experience a major earthquake than heretofore believed.
Joint inversion of gravity and magnetic anomalies of eastern Canada
Authors: Zheng Ying , Arkani-Hamed Jafar
Published: April 2011

The power spectra and degree correlation of the surface topography and free-air gravity anomalies of eastern Canada show that the gravity anomalies are subdivided into three parts. The short-wavelength components (30-170 km, shorter than 30 km are not well resolved) largely arise from density perturbations in the crust and to a lesser extent from the surface topography and Moho undulation, whereas the contribution of intracrustal sources to the intermediate-wavelength components (170-385 km) is comparable with that of the topography. The long-wavelength components (385-1536 km) are overcompensated at the Moho. We present a crustal model for the intermediate- and long-wavelength components which takes into account the surface topography, density perturbations in the crust, and Moho undulation with a certain degree of isostatic compensation. The general characteristics of this model resemble the crustal structure revealed from seismic measurements. The reduced-to-pole magnetic anomalies of eastern Canada show no pronounced correlation with the topography and with the vertical gradient of the gravity anomalies, suggesting that the source bodies are within the crust and Poisson's relationship does not hold over the entire area. Assuming that the magnetic anomalies arise from induced magnetization, lateral variations of magnetic susceptibility of the crust are determined while taking into account the effects of the surface topography and the Moho undulation of our crustal model. The intermediate- and long-wavelength components of the susceptibility contrasts delineate major collision zones as low-susceptibility regions. We interpret this in terms of thermal demagnetization of the high-magnetic crustal roots beneath the collision zones.
Epistrenoceras Bentz (Ammonoidea) from the Middle Jurassic of Kutch (western India): a new record and its chronostratigraphic implication
Authors: Kayal A , Bardhan S
Published: April 2011

The identification of late Bathonian beds and the position of the boundary between the Bathonian and Callovian in Kutch, western India, continued to be elusive until recently. The dominant ammonite faunas show strong endemism and thus are of little value in worldwide age correlations. The present paper records Epistrenoceras Bentz from the Patcham Formation of Jumara, which is regarded as a biological stopwatch indicating only the upper Bathonian. This find, together with other recently recorded time-diagnostic forms, now resolves the uncertainties.
An improved velocity model for the crust and upper mantle along the central mobile belt of the Newfoundland Appalachian orogen and its offshore extension
Authors: Chian Deping , Marillier François , Hall Jeremy , Quinlan Garry
Published: April 2011

New modelling of wide-angle reflection-refraction data of the Canadian Lithoprobe East profile 91-1 along the central mobile belt of the Newfoundland Appalachian orogen reveals new features of the upper mantle, and establishes links in the crust and upper mantle between existing land and marine wide-angle data sets by combining onshore-offshore recordings. The revised model provides detailed velocity structure in the 30-34 km thick crust and the top 30 km of upper mantle. The lower crust is characterized by a velocity of 6.6-6.8 km/s onshore, increasing by 0.2 km/s to the northeast offshore beneath the sedimentary basins. This seaward increase in velocity may be caused by intrusion of about 4 km of basic rocks into the lower crust during the extension that formed the overlying Carboniferous basins. The Moho is found at 34 km depth onshore, rising to 30 km offshore to the northeast with a local minimum of 27 km. The data confirm the absence of deep crustal roots under the central mobile belt of Newfoundland. Our long-range (up to 450 km offset) wide-angle data define a bulk velocity of 8.1-8.3 km/s within the upper 20 km of mantle. The data also contain strong reflective phases that can be correlated with two prominent mantle reflectors. The upper reflector is found at 50 km depth under central Newfoundland, rising abruptly towards the northeast where it reaches a minimum depth of 36 km. This reflector is associated with a thin layer (1-2 km) unlikely to coincide with a discontinuity with a large cross-boundary change in velocity. The lower reflector at 55-65 km depths is much stronger, and may have similar origins to reflections observed below the Appalachians in the Canadian Maritimes which are associated with a velocity increase to 8.5 km/s. Our data are insufficient for discriminating among various interpretations for the origins of these mantle reflectors.
Controls and age of cavernous porosity in Middle Silurian dolomite, southern Ontario
Authors: Kunert Micheal , Coniglio Mario , Jowett E Craig
Published: April 2011

Porosity in bioclastic dolomites of the Amabel Formation in the Eramosa River area, northeast of Guelph, Ontario, is characterized by solution-enlarged joints in outcrop (kluftkarren), and vuggy and cavernous intervals in the subsurface. In addition, a network of accessible caves has been dissected by Recent fluvial incision by the present Eramosa River valley. Porosity development was controlled locally by lithostratigraphy and regionally by the progressive downcutting of a deeply incised, buried bedrock valley west of Rockwood. The Amabel Formation is capped by the Eramosa Member of the Guelph Formation, which consists of jointed but relatively nonporous, laminated to medium-bedded, bituminous dolomitized mudstones. The vuggy and cavernous porosity in the Amabel Formation is probably pre-Wisconsinan to Early Wisconsinan in age, beginning more than 60-75 ka, and developed in response to the lowering of hydraulic gradients as the channel of the Rockwood buried valley was progressively incised. Porous intervals at higher elevations were abandoned in favour of deeper flow paths as incision continued, creating a complex gallery of interconnected subsurface conduits. Subsequent ice advances and ablation events eventually filled the valley with tills and interglacial sands and gravels, ending the valley's influence on the development of vuggy and cavernous porosity.
Paleomagnetism and U-Pb geochronology of diabase dyke swarms of Minto block, Superior Province, Quebec, Canada
Authors: Buchan Kenneth L , Mortensen James K , Card Kenneth D , Percival John A
Published: April 2011

In the first collaborative study of paleomagnetism and precise U-Pb geochronology in the Minto block of the Superior Province, mafic dyke swarms with three widely divergent paleomagnetic signatures and isotopic ages have been identified. The 2505 ± 2 Ma Ptarmigan dykes trend north to northeast and have a virtual geomagnetic pole at 42°S, 220°E, similar to that of 2473-2446 Ma Matachewan dykes of the southern Superior Province. The ca. 2230 Ma Maguire dykes trend west to northwest and yield a paleopole at 9°S, 267°E, similar to those for 2216+8-4 Ma Senneterre dykes and 2217-2210 Ma Nipissing sills of the southern Superior and Southern provinces, respectively. The 2209 ± 1 Ma Klotz dykes trend west-northwest, but do not carry a consistent magnetization direction. Finally, 1998 ± 2 Ma Minto dykes of west-northwest to northwest trend, identical in age to the 1998 Ma ± 2 Ma Purtuniq ophiolite of the Cape Smith Belt, have a paleopole at 38°N, 174°E. The similarity of paleopoles for the ca. 2.23-2.21 Ga Maguire dykes of the Minto block, Senneterre dykes of the southern Superior, and Nipissing sills of the Southern Province demonstrates that these regions were in their present relative latitudes and orientations at that time. Likewise, the similarity of the Ptarmigan virtual geomagnetic pole and the Matachewan paleopole suggests little relative latitudinal movement or rotation of the two regions since ca. 2.5 Ga. The Maguire, Senneterre, and Klotz dykes form a roughly radiating pattern and may represent one quadrant of a giant radiating dyke swarm centred southeast of Ungava Bay, whose focus marks the location of a mantle plume responsible for ca. 2.22 Ga breakup along the eastern margin of the Superior Province. If so, the coeval Nipissing sills that intrude sedimentary rocks of the Huronian Supergroup of the Southern Province may have been fed laterally by Senneterre dykes from the Ungava plume centre.
Depth of emplacement and tilting of the Middle Proterozoic (1470 Ma) Wolf River batholith, Wisconsin: 40Ar/39Ar thermochronologic constraints
Authors: Holm Daniel , Lux Daniel
Published: April 2011

The 1470 Ma Wolf River batholith of northeastern Wisconsin is one of the oldest and largest intrusive sequences of the Middle Proterozoic magmatic suite that trends across the continent from Labrador to southern California. The presence of miarolitic cavities in portions of the batholith and in associated plutons (Wausau syenite complex) and equilibrium considerations suggest a shallow emplacement depth (i.e., <4 km). However, these data contrast with published Rb/Sr biotite ages, which suggest much of the batholith was uplifted through mid-crustal temperatures well after intrusion. To address this problem better, we have obtained four biotite 40Ar/39Ar dates from a transect across the southwestern portion of the batholith, one date from the ~1520 Ma Wausau syenite complex, and another from rocks metamorphosed during the Early Proterozoic Penokean orogeny. The two oldest dates are concordant (within error) with the crystallization age of the batholith, suggesting rapid cooling after intrusion and hence shallow emplacement depth. Cooling dates young to the south-southeast, however, and the youngest dates within the batholith (~1400 Ma) are concordant with previous Rb/Sr biotite dates and with the Ar/Ar biotite date from the adjacent country rock. The data suggest slow cooling and southeast-side-up tilting of this portion of the exposed batholith from mid-crustal temperatures (~300°C). Postemplacement uplift and tilting of the batholith appear related to differential isostatic uplift driven by substantial original thickness variations of the intrusion.
Very high temperature, moderate pressure metamorphism in the New Russia gneiss complex, northeastern Adirondack Highlands, metamorphic aureole to the Marcy anorthosite
Authors: Alcock J , Muller Peter
Published: April 2011

The New Russia gneiss complex in the northeastern Adirondack Highlands of New York includes meta-anorthosite gneiss and anatectic gneiss derived from metagabbro, mangerite, and charnockite. Metamorphic conditions during anatexis (850-950°C, highest near the anorthosite, with pressure ~750 MPa) are inferred from minerals and textures produced by dehydration melting of pargasitic hornblende and from ternary feldspar in anatectic segregations. The complex abuts and is crosscut by the eastern margin of the ~1130 Ma Marcy anorthosite massif. The crosscutting contact, the presence of meta-anorthosite gneiss within the complex and undeformed meta-anorthosite in the massif, and the occurrence of deformed and undeformed anatectic segregations within the New Russia gneisses indicate an approximate synchroneity of penetrative deformation, very high temperature metamorphism, and emplacement of anorthosite with both intrusion and anatexis outlasting deformation. The position of the New Russia gneisses, the metamorphic gradient within them, and the contemporaneity of anatexis with intrusion of anorthosite imply that the complex is the metamorphic aureole of the Marcy anorthosite.
Detrital and metamorphic 40Ar/39Ar ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia
Authors: Hicks Roberta J , Jamieson Rebecca A , Reynolds Peter H
Published: April 2011

40Ar/39Ar dates from eight muscovite separates and two whole-rock samples of slate, siltstone, and sandstone provide detrital, metamorphic, and post-metamorphic overprinting ages for the low-grade metamorphic rocks of the Meguma Supergroup in the Mahone Bay region of southern Nova Scotia. Variably reset detrital muscovite ages of 600-550 Ma agree with previously obtained U-Pb dates from detrital zircon. Separates of foliation-parallel muscovite yield precise 40Ar/39Ar ages of 395-388 Ma. Petrographic and metamorphic data indicate that these are metamorphic mica growth ages. The range overlaps with the younger limit of previously reported whole-rock ages (410-380 Ma), but is more tightly constrained. An apparent inconsistency between previous 40Ar/39Ar whole-rock ages as old as 410 Ma and regional deformation that affected sedimentary rocks as young as 385 Ma has been resolved by the younger ages reported here and by recent adjustments to the early Paleozoic time scale which suggest that the Lochkovian to Emsian Torbrook Group was deposited between 419 and 394 Ma. A muscovite plateau age of 376 Ma from one sample may be related to late-stage flexural slip deformation in the Ovens gold district.
Coeval sedimentation, magmatism, and fold-thrust belt development in the Trans-Hudson Orogen: geochronological evidence from the Wekusko Lake area, Manitoba, Canada
Authors: Ansdell Kevin M , Connors Karen A , Stern Richard A , Lucas Stephen B
Published: April 2011

Lithological and structural mapping in the east Wekusko Lake area of the Flin Flon Belt, Trans-Hudson Orogen, suggested an intimate relationship between magmatism, fluvial sedimentation, and initiation of fold and thrust belt deformation. Conventional U-Pb geochronology of volcanic rocks in fault-bounded assemblages provides a minimum age of 1876 ± 2 Ma for McCafferty Liftover back-arc basalts, and ages of between 1833 and 1836 Ma for the Herb Lake volcanic rocks. A rhyolite which unconformably overlies Western Missi Group fluvial sedimentary rocks has complex zircon systematics. This rock may be as old as about 1856 Ma or as young as 1830 Ma. The sedimentary rocks overlying this rhyolite are locally intercalated with 1834 Ma felsic volcanic rocks, and yield sensitive high resolution ion microprobe (SHRIMP) U-Pb and Pb-evaporation detrital zircon ages ranging from 1834 to 2004 Ma. The Eastern Missi Group is cut by an 1826 ± 4 Ma felsic dyke, and contains 1832-1911 Ma detrital zircons. The dominant source for detritus in the Missi Group was the Flin Flon accretionary collage and associated successor arc rocks. The fluvial sedimentary rocks and the Herb Lake volcanic rocks were essentially coeval, and were then incorporated into a southwest-directed fold and thrust belt which was initiated at about 1840 Ma and active until at least peak regional metamorphism.
Coeval sedimentation, magmatism, and fold-thrust development in the Trans-Hudson Orogen: propagation of deformation into an active continental arc setting, Wekusko Lake area, Manitoba
Authors: Connors Karen A , Ansdell Kevin M , Lucas Stephen B
Published: April 2011

Early structures in the southeastern part of the Trans-Hudson Orogen (THO), Wekusko Lake area, Manitoba, comprise northwest-verging folds and a set of steep, southeast-dipping faults that occur at a low angle to bedding. Kinematic indicators are rare, however, the vergence of the associated folds supports reverse movement on the faults. These folds and faults formed prior to the peak of regional metamorphism and therefore must correlate with the widely recognised deformational (D2) event which developed pre- to syn-metamorphism and involved development of a regional, south- to southwest-directed fold-thrust belt. The D2 folds and reverse faults in the study area are interpreted to have originally formed as gently dipping, southwest-verging structures, i.e., as inclined folds and thrust faults, which were then rotated into a steep, northwest-verging orientation during later deformation (D3). In the southeastern THO, regional D2 fold and thrust structures are cut by ca. 1839-1830 Ma plutons, indicating that D2 initiated prior to ca. 1839 Ma. Recognition of these structures in the study area, and their relationships to key stratigraphic units, has provided significant insights into the tectonic setting during the regional D2 event. The D2 fold and thrust structures deform ca. 1834 Ma fluvial sedimentary rocks and ca. 1836-1832 Ma volcanic (subaerial) and plutonic rocks with a "continental" arc geochemical signature. These are the youngest known volcanic and sedimentary rocks within the THO. The subaerial deposition of these young rocks was coeval with initiation of D2 deformation in the region. They were then rapidly incorporated into the thrust fault sequence soon after their formation, which suggests that the fold and thrust structures propagated into a zone of active magmatism which must have been located in the foreland to the belt of thrusting and folding.
Polyphase deformation and crustal evolution in the Pipestone Lake area of the Archean Wabigoon Subprovince, Superior Province, Canada
Authors: Edwards Garth R , Stauffer Mel R
Published: April 2011

Archean supracrustal rocks in the western Wabigoon Subprovince, Superior Province, Canadian Shield, have undergone four phases of deformation, D1-D4. D1, confined to the oldest rocks, includes a large, refolded, reclined, isoclinal anticline (F1) with moderately developed axial-planar cleavage (S1). Rocks affected by D1 are overlain by a regional unconformity. D2 includes post-unconformity, steeply plunging, north-northeast-south-southwest-striking, isoclinal folds (F2) that are approximately coaxial with F1, but have contorted the F1 axial trace. D3 is represented by east-west-striking, steeply plunging folds at various scales (F3) which occur mainly in rocks near the regional Manitou Stretch - Pipestone Lake Shear Zone, also interpreted to be a D3 structure. D4 is represented by pervasive cleavage (S4), locally penetrative but mainly spaced, including crenulation cleavage, fractures, small faults, and brittle-ductile shears. S4 is parallel to the margin of the Jackfish Lake Pluton. D1-D3 are ascribed to convergence of the Wabigoon Subprovince with adjacent subprovinces, ending with formation of the Manitou Stretch - Pipestone Lake Shear Zone as a (presently) steep thrust and oblique-ramp structure. D4 is the result of either diapiric emplacement of the Jackfish Lake Pluton, or marginal strain intensification due to the rigidity of the older Ash Bay Dome during late north-south compression. Previously available zircon U-Pb geochronology provides a maximum age for D1 of 2728 Ma, and an approximate age for D4 of 2698 Ma. The unconformity developed between D1 and D2, 2725-2713 Ma.