Cooperative seismic surveys across the Superior–Churchill boundary zone in southern Canada

Green, A. G.; Stephenson, O. G.; Mann, G. D.; Kanasewich, E. R.; Cumming, G. L.; Hajnal, Z.; Mair, J. A.; West, G. F.

doi:10.1139/e80-059

Cited by 34 publications

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“…The weighted means are high and represent a 0.2-0.3 km/s increase in Vp at 600 MPa relative to the WGT. A velocity increase of this magnitude was predicted by Percival [ 1986] based on density and is similar to the velocity contrast observed by seismic refraction across the Conrad discontinuity at several locations in the Canadian and Baltic shields [e.g., Berry and Fuchs, 1973;Hall and Hajnal, 1973;Green et al, 1979Green et al, , 1980Luosto and Korhonen, 1986;Grad and Luosto, 1987;Morel-g-l'Huissier et al, 1987;Boland et al, 1988;Boland and Ellis, 1989]. Thus the transition from the WGT to the KSZ may represent an exposed example of a midcrustal discontinuity, such as the Conrad, in shield regions.…”

Section: For Reference the Various Linear Velocity-density Relationsupporting

confidence: 69%

Seismic structure of the continental crust based on rock velocity measurements from the Kapuskasing Uplift

Fountain¹,

Salisbury²,

Percival³

1990

J. Geophys. Res.

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The Michipicoten greenstone belt (MGB), Wawa gneiss terrane (WGT), and Kapuskasing structural zone (KSZ) in Ontario, Canada, are regarded as a 25‐km‐thick partial cross section through the crust of the Superior Province. We measured compressional wave velocities (Vp) at confining pressures up to 600 MPa for representative rock samples from these terranes. Vp for MGB is variable (6.1–7 km/s) and depends on composition and anisotropy. Compressional wave velocities for low anisotropy quartzofeldspathic gneisses and intrusive rocks from the WGT and the KSZ show little variation over a wide range of silica content but mafic gneisses and anorthositic rocks show a wide velocity range over a narrower silica range, a trend corroborated by data for other high‐grade rocks. A model of the continental crust based on the laboratory data shows three megalayers with differing seismic characteristics. The shallowest levels (MGB) are seismically heterogeneous with high average velocities (6.6 km/s at 100 MPa) because of the dominance of metabasalts. The balance of the upper crust (WGT) is seismically homogeneous as it is dominated by a variety of isotropic quartzofeldspathic rocks with average velocities of 6.35 km/s at 100 MPa and 6.6 km/s at 600 MPa. The uppermost lower crust (KSZ) is layered, seismically heterogeneous and transversely isotropic. The average velocity at 600 MPa is 6.84 km/s. The boundary between WGT and KSZ is marked by a velocity increase of between 0.2 and 0.3 km/s, an increase similar to that commonly associated with midcrustal discontinuities (i.e., Conrad) in shield areas. Here, this boundary corresponds to the amphibolite‐granulite facies transition and to a change from a tonalitic middle crust to a lithologically heterogeneous uppermost lower crust. Refraction results show an anomalous high‐velocity zone in the upper crust under the KSZ that, on the basis of laboratory velocity data, can be correlated with KSZ lithologies. These data indicate that KSZ rocks can be traced to the west to depths as great as 20 km. Levels deeper than 20 km, not exposed at the surface in the KSZ, are characterized by velocities greater than 7.0 km/s and may be dominated by mafic and anorthositic lithologies or by more garnet‐rich rocks. The velocity model of the Superior Province crust based on geological reconstruction and laboratory velocity data is in general agreement with the velocity structure to depths of about 25 km determined for the crust below the MGB from refraction experiments. The velocity structure of this model is also generally similar to the velocity structure of shield areas.

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Section: For Reference the Various Linear Velocity-density Relationsupporting

confidence: 69%

Seismic structure of the continental crust based on rock velocity measurements from the Kapuskasing Uplift

Fountain¹,

Salisbury²,

Percival³

1990

J. Geophys. Res.

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“…With the introduction of a 7 km/s layer at the base of the line A model (Figures 2e and 10) it is no longer necessary to invoke a major thickening of the crust at the edge of the Superior craton [Green et al, 1980]. Instead, our modeling shows that the thickness of the crust varies smoothly from near the Superior craton margin across the Trans-Hudson orogen to the Wyoming craton (Figures 10 and 11).…”

Section: East-west Linementioning

confidence: 87%

Crustal refraction surveys across the Trans‐Hudson Orogen/Williston Basin of south central Canada

Morel-à-l'Huissier¹,

Green²,

Pike³

1987

J. Geophys. Res.

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Eight reversed seismic refraction profiles have been recorded across the Phanerozoic Williston sedimentary basin that overlies the margins of the Superior and Wyoming Arcbean cratons and the Proterozoic Trans-Hudson orogen. These clata have been modeled using two-dimensional ray-tracing techniques to match the times and amplitudes of primary and coherent secondary arrivals. Within the southern extension of the Superior craton margin (Thompson belt) a high-velocity (•6.4 km/s) lid overlies a narrow region of high electrical conductivity, and a zone of westerly dipping reflections is nearly coincident with a weak velocity discontinuity that seems to delineate the western edge (Thompson fault) of the craton margin. Complex zones of low-velocity material and the North American Central Plains electrical conductivity anomaly are concluded to lie within the southern extension of the Reindeer-South Indian Lakes terrain, a component of the Trans-Hudson orogen. A high-velocity (•> 7.0 km/s) lower crustal layer, which represents a zone of complexity separating "normal" crust from the upper mantle, extends throughout the region. The crust is relatively thick, with depths to Moho varying smoothly between 41 and 48 km. There is no evidence in the relatively low-resolution seismic refraction data for abrupt changes in the level of the Moho, but there may be a minor (3-4 km) thinning of the crust near the center of the Williston Basin. iments were the eastern edge of the Superior craton, the Trans-Hudson orogen [Hoffman, 1981], the North American Central Plains (NACP) electrical conductivity anomaly [Camfield and Gough, 1977], and the Williston Basin. During the three field campaigns, approximately 2250 km of reversed inline refraction data were collected along eight profiles arranged in the following geometry: (1) four N-S lines (A, C, D, and E), three of which were parallel to the major tectonic axes of the buried Precambrian shield, (2) three lines (E, F, and G) in a triangular configuration (included one of the N-S lines), and (3) two E-W lines (B and H) that cut across the axis of the Trans-Hudson orogen and that connected most of the other lines. Fan shooting into the three sides of the equilateral triangle E, F, and G was also performed. Preliminary analyses of parts of these data have been published by Green et al. [1980], Delandro and Moon [1982], Hajnal et al. [1984], and Kanasewich and Chiu [1985]. The interpretation of lines A and B by Green et al. [1980] was based on inversions of first arrival times assuming simple dipping models and synthetic seismogram analyses using the Fuchs and Muller [1971] reflectivity algorithm. Delandro and Moon's [1982] interpretation of the same lines incorporated slightly more complex structures using the Whittall and Clowes [1979] two-dimensional ray-tracing program and the WKBJ method for calculating one-dimensional synthetic seimograms [Chapman, 1978]. The interpretation of lines C, D, • Now at Texaco Canada Resources, and H (western shot) by Hajnal et al. [1984] was based on one-dim...

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“…3). On the eastern side, COCRUST obtained lines A and B in 1977, while lines C, D, and the western shot of line H were obtained in 1979 (Green et al 1980;Hajnal et al 1984). The final sequence was completed in 1981 when COCRUST obtained lines E, F, G, and H. In all, over 2200 km of reversed refraction data are available in the area.…”

Section: Data Acquisition and Processingmentioning

confidence: 97%

Seismic studies of the crust under the Williston Basin

Kanasewich¹,

Hajnal²,

Green³

et al. 1987

Can. J. Earth Sci.

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The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around the basin as well as define the properties of the various terranes of the Hudsonian mobile belt.La mCthode de sismique refraction a Ct C utilisCe en 1981 pour Ctudier la croQte sous la moitiC nord du bassin de Williston, en Saskatchewan. Une nouvelle mCthode d'enregistrement de sismique spatiale, basCe sur une disposition triangulaire des rCcepteurs, a Ct C utiliske pour la premikre fois dans-le but de d~terminef la $ructure en trois dimensions et d'estimer les vitesses des ondes. La sismique refraction par le travers et les donnCes de kflexion a grand angle obtenues par cette technique ont Ct C particulitrement utiles pour dCfinir plusieurs blocs faillts. Ces blocs sont Cgalement caractCrisCs par des anomalies aCromagnCtiques de directions onentees prCfCrentiellement vers le nod. L'Cpaisseur de la croate dans la partie sud des provinces de 1'Ouest pksente de fortes variations allant de 35 i 3 50 km. Une bonne partie de la rCgion se distingue Cgalement par la pksence d'une ou plusieurs couches de vitesses faibles et par une vitesse rapide dans la croate infkrieure. Les ksultats suggkrent fortement une hCtCrogCneitC latCrale significative et les Ctudes dCtaillCes de la sismique kflexion et kfiaction de profondeur sembleraient fournir des renseignements fiables sur les attitudes des couches et des failles autour du bassin en plus de dCfinir les propriCtCs des divers terranes de la zone mobile de llHudsonien.[Traduit par la revue]Can.

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Cooperative seismic surveys across the Superior–Churchill boundary zone in southern Canada

Cited by 34 publications

References 0 publications

Seismic structure of the continental crust based on rock velocity measurements from the Kapuskasing Uplift

Seismic structure of the continental crust based on rock velocity measurements from the Kapuskasing Uplift

Crustal refraction surveys across the Trans‐Hudson Orogen/Williston Basin of south central Canada

Seismic studies of the crust under the Williston Basin

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