Seismic investigation of the Coast Plutonic Complex – Insular Belt boundary beneath the Strait of Georgia

1984 ◽  
Vol 21 (9) ◽  
pp. 1033-1049 ◽  
Author(s):  
Donald J. White ◽  
Ron M. Clowes
Keyword(s):  
Crustal Structure ◽  
Seismic Refraction ◽  
Unconsolidated Sediments ◽  
The West ◽  
Strait Of Georgia ◽  
Seismic Properties ◽  
Air Gun ◽  
Plutonic Complex ◽  
Major Fault ◽  
Coast Plutonic Complex

The Strait of Georgia, a topographic depression between Vancouver Island and the mainland of British Columbia, is considered to be the boundary between two tectonic provinces: the Coast Plutonic Complex on the east and the Insular Belt to the west. The allochthonous nature of the Insular Belt has been established, mainly on the basis of paleomagnetic measurements. Various tectonic models to explain the geological differences between the two provinces have been proposed. One of these suggests that the boundary is an old transform fault zone and is represented currently by a thrust fault along the eastern side of the Strait of Georgia. Other models propose that the Coast Plutonic Complex is a feature superimposed by tectonic and metamorphic events after the accretion of the Insular Belt. Such models do not require a major crustal discontinuity along the Strait of Georgia.In May 1982, a seismic refraction survey using a 32 L air gun and a radio telemetering sonobuoy system was carried out in the Strait of Georgia with the objective of investigating the nature of this boundary and determining the upper crustal structure. Three reversed profiles across the strait were shot; these are supplemented by several high-resolution reflection profiles from previous experiments. Two-dimensional models of the crustal structure across the strait have been constructed using a forward modelling ray trace and synthetic seismogram algorithm to match the travel times and amplitude characteristics of the data.Three basic layers or strata form the models, for which the maximum depth of reliability is 3 km. The first layer consists of unconsolidated sediments and Pleistocene glacial deposits, and the second represents Late Cretaceous – early Tertiary basin fill sediments that form the Nanaimo Group, the Burrard–Kitsilano formations, and the Chuckanut Formation. The third layer is likely the extension of the Coast Plutonic Complex beneath the strait, but the westerly limit of this unit is undetermined because of seismic properties similar to those of the Insular Belt volcanics. A local fault is located ~15 km northeast of Galiano Island on the west side of the strait. However, our study shows no evidence for a major fault along the strait. Thus those aspects of tectonic models that require the existence of a major transform or transcurrent fault boundary along the Strait of Georgia. may have to be revised.

High-precision U–Pb geochronology of the Butedale pluton, British ColumbiaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 557-565 ◽  
Author(s):  
Steven W. Denyszyn ◽  
Roland Mundil ◽  
Sarah J. Brownlee ◽  
Paul R. Renne
Keyword(s):  
High Precision ◽  
Thermal History ◽  
Thermal Ionization Mass Spectrometry ◽  
Pacific Coast ◽  
Test Case ◽  
Ionization Mass ◽  
The West ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Single Grain

The Butedale pluton, a ca. 100 km long compositionally zoned batholith, is part of the Coast Plutonic Complex that extends the length of the Canadian Pacific coast. Its age and thermal history are relevant to the Butedale pluton’s role as a test case of the Baja–BC hypothesis, as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the Coast Shear Zone. High-resolution U–Pb (chemical abrasion – thermal ionization mass spectrometry (CA–TIMS), zircon) analysis of rocks across the width of the Butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the West Butedale pluton (ca. 95 Ma) and the East Butedale pluton (ca. 85 Ma). The East Butedale pluton was reheated by the emplacement of a younger adjacent pluton, which may have caused partial Pb loss and resulting excess scatter of 206Pb/238U zircon ages within individual samples. The West Butedale pluton may be the same age as, and part of, the nearby Ecstall pluton, thereby doubling the length of the Ecstall pluton to ca. 200 km. Single-grain, high-precision U–Pb analysis of zircon reveals previously unknown complexity and detail of emplacement and thermal history in the Butedale plutons.

Structure of the Canadian Cordillera from Seismic Refraction and Other Data

1975 ◽  
Vol 12 (2) ◽  
pp. 182-208 ◽  
Author(s):  
M. J. Berry ◽  
D. A. Forsyth
Keyword(s):  
Seismic Data ◽  
Seismic Refraction ◽  
Vancouver Island ◽  
Geological Structure ◽  
Canadian Cordillera ◽  
Low Velocity ◽  
Model Calculations ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Crustal Density

A synthesis of Canadian Cordilleran refraction data recorded prior to 1971 with other geophysical data shows major features which correlate well with the regional geological structure. The wavelength of M topography decreases from about 200 km at 54°N to about 110 km at 52°N and culminates in a major lithospheric discontinuity east of Vancouver Island. The seismic data indicate the region of the Fraser River at Quesnel, the region immediately east of and parallel to the Coast Plutonic Complex and possibly the western edge of the Hazelton Mountains are sites of significant changes in lithospheric structure.Lateral variations in the average crustal density are necessary to reconcile both gravity and seismic data. The crust beneath the central, intermontane region is characterized by a mass deficiency, whereas the density of the crust beneath Vancouver Island appears greater than average.Calculation of synthetic record sections shows that the Pn phase may propagate considerably beyond crossover in a layer a few wavelengths thick. A model for the Canadian Cordillera which includes a low velocity layer as little as 8 km below the M appears plausible. Model calculations suggest that the M approximates a discontinuity beneath the Coast Plutonic Complex, but is better modelled as a transition zone beneath the Omineca Crystalline belt.

Crustal structure of NW British Columbia and SE Alaska from seismic wide-angle studies: Coast Plutonic Complex to Stikinia

2000 ◽  
Vol 105 (B4) ◽  
pp. 7961-7981 ◽  
Author(s):  
Philip T. C. Hammer ◽  
Ron M. Clowes ◽  
Robert M. Ellis
Keyword(s):  
British Columbia ◽  
Crustal Structure ◽  
Wide Angle ◽  
Plutonic Complex ◽  
Coast Plutonic Complex

scholarly journals The crustal structure of the Northeast Greenland continental shelf across the extension of the West Jan Mayen Fracture Zone

2020 ◽  
Author(s):  
Thomas Funck ◽  
Andreas Skifter Madsen ◽  
Christian Berndt ◽  
Anke Dannowski ◽  
Dieter Franke ◽  
...  
Keyword(s):  
Continental Margin ◽  
Crustal Structure ◽  
Fracture Zone ◽  
Seismic Refraction ◽  
Moho Depth ◽  
Gravity Modeling ◽  
The South ◽  
The West ◽  
The North ◽  
Lower Crustal

<p>Between August and October 2017, the German research vessel Maria S. Merian acquired geophysical data along the Northeast Greenland continental margin during its cruise MSM-67. This included seismic reflection and wide-angle/refraction data as well as potential field data. In comparison to the conjugate mid-Norwegian margins, the Northeast Greenland continental margin is less well studied. Hence, one of the key objectives of the expedition was to improve the understanding of the opening of the Northeast Atlantic Ocean and the evolution of the conjugate margin pair. One particular goal of the experiment was the mapping of the lateral extent of magmatism associated with the opening and how this relates to margin segmentation.</p><p>Seismic refraction line BGR17-2R2 runs on the shelf and parallel to the coast of NE Greenland. It crosses the landward extension of the West Jan Mayen Fracture Zone that separates the seafloor spreading along the Mohn’s Ridge in the north from the Kolbeinsey Ridge in the south. A total of 29 ocean bottom seismometers (OBS) equipped with a hydrophone and three-component geophones were deployed along the 235-km-long line. The seismic source was a G-gun array with a total volume of 4840 cubic inches (79.3 L) fired every 60 s. In the central and northern part of the line, two older seismic refraction profiles are crossed (lines AWI2003-500 and 400, respectively), which run perpendicular to the margin and can be used for lateral correlation of the crustal structure.</p><p>For the initial analysis, a velocity model was developed by forward and inverse modeling of travel times using the program RAYINVR. Later, a travel time tomography was carried out employing the code Tomo2D and performing a Monte Carlo analysis with 100 inversions from which an average model was calculated. The models show a 1-to 3-km-thick sedimentary column with velocities ranging from 1.6 to 4.0 km/s. In the central and northern part, a 1-km-thick layer with velocities around 4.6 km/s is underlying the sediments and is interpreted to consist of volcanic material. Below and extending along the entire length of the line, velocities of 5.6 km/s are observed in a layer that is ~2 km thick. The crystalline basement has a depth around 5 km with higher velocities in the north (6.5 km/s) than in the south (6.3 km/s). High lower crustal velocities (>7.2 km/s) are observed along the entire line and either indicate magmatic underplating or lower crustal sill intrusions. The Moho depth is seismically constrained along the central part of the line where it is 30 km. Gravity modeling suggest a depth of 35 and 27 km at the southern and northern limit of the profile, respectively. Within the zone of the landward extension of the West Jan Mayen Fracture Zone, a decrease in mid-crustal velocities by 0.2 km/s is observed. Slightly to the north of the fracture zone, a 50-km-wide zone with increased mid-and lower crustal velocities may indicate an igneous center in an area where the upper volcanic layer is shallowest.</p>

Crustal structure of the Nova Scotian margin in the Laurentian Channel region

1987 ◽  
Vol 24 (9) ◽  
pp. 1859-1868 ◽  
Author(s):  
I. Reid
Keyword(s):  
Crustal Structure ◽  
Seismic Velocity ◽  
Structural Information ◽  
Seismic Refraction ◽  
Ocean Bottom ◽  
Eastern Canada ◽  
Crustal Layer ◽  
Air Gun ◽  
Lower Crustal

A seismic-refraction study on the outer Scotian Shelf of eastern Canada, carried out using large air-gun sources and ocean bottom seismograph receivers, has provided structural information on the entire crustal column. A thick (about 13 km) sedimentary sequence is characterized by significant lateral variation in this area, and a marked increase in seismic velocity around 8 km depth may delineate the synrift–postrift transition. Beneath the sediments is highly attenuated continental crust, about 11 km thick, with some evidence for a lower crustal layer of velocity around 7 km/s, which may be partly due to under-plating during rifting. Determination of the complete crustal structure, including the tentative delineation of the rift–drift transition, in a region of large crustal extension provides a useful test for models of continental rifting, and a simple uniform extension–subsidence model is found to produce an adequate fit to the interpreted structure.

Crustal structure across the Nain – Makkovik boundary on the continental shelf off Labrador from seismic refraction data

1996 ◽  
Vol 33 (3) ◽  
pp. 460-471 ◽  
Author(s):  
Ian Reid
Keyword(s):  
Continental Shelf ◽  
Wave Velocity ◽  
Crustal Structure ◽  
Lower Crust ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
P Wave ◽  
Air Gun ◽  
P Wave Velocity

A detailed seismic refraction profile was shot along the continental shelf off Labrador, across the boundary between the Archean Nain Province to the north and the Proterozoic Makkovik orogenic zone to the south. A large air-gun source was used, with five ocean-bottom seismometers as receivers. The data were analysed by forward modelling of traveltimes and amplitudes and provided a well-determined seismic velocity structure of the crust along the profile. Within the Nain province, thin postrift sediments are underlain by crust with a P-wave velocity of 6.1 km/s, which increases with depth and reaches 6.6 km/s at about 8 km. Moho is at around 28 km, and there is no evidence for a high-velocity (>7 km/s) lower crust. The P- and S-wave velocity structure is consistent with a gneissic composition for the Archean upper crust, and with granulites becoming gradually more mafic with depth for the intermediate and lower crust. In the Makkovik zone, the sediments are thicker, and a basement layer of P-wave velocity 5.5–5.7 km/s is present, probably due to reworking of the crust and the presence of Early Proterozoic volcanics and metasediments. Upper crustal velocities are lower than in the Nain Province. The crustal thickness, at 23 km, is less, possibly due in part to greater crustal stretching during the Mesozoic rifting of the Labrador Sea. The crustal structure across the Nain–Makkovik boundary is similar to that across the corresponding Archean–Ketilidian boundary off southwest Greenland.

A seismic refraction and gravity study of the earth's crust in British Columbia

1965 ◽  
Vol 55 (2) ◽  
pp. 463-486 ◽  
Author(s):  
W. R. H. White ◽  
J. C. Savage
Keyword(s):  
British Columbia ◽  
West Coast ◽  
Coastal Area ◽  
Intermediate Layer ◽  
Seismic Refraction ◽  
East Side ◽  
The West ◽  
Strait Of Georgia ◽  
Large Explosion ◽  
Upper Boundary

Abstract Explosion refraction studies have been carried out in areas adjacent to Vancouver Island, including the Strait of Georgia and Johnstone Strait and along the west coast of the Island. A refraction line has also been observed from a large explosion in Seymour Narrows, eastward through the mountains and for some distance across the plains of Alberta. Although the surficial strata complicate the interpretation, a series of short refraction profiles consistently reveal the presence of an intermediate layer with velocity of about 6.8 km/sec. in the coastal area. The depth to the upper boundary of this layer varies from about 11 km. along the west coast of the Island to less than 5 km. in the Strait of Georgia and along the east side of the Island. The longer range observations parallel to the coast indicate this layer to be more than 40 km. thick. On the profile eastward through the mountains a velocity of 7.8 km/sec. has been found for Pn, from an unreversed profile, with a crustal thickness of approximately 30 km.

Crustal structure of the Reykjanes Ridge near 62°N, on the basis of seismic refraction and gravity data

2007 ◽  
Vol 43 (1) ◽  
pp. 55-72 ◽  
Author(s):  
Wolfgang R. Jacoby ◽  
Wilfred Weigel ◽  
Tanya Fedorova
Keyword(s):  
Crustal Structure ◽  
Gravity Data ◽  
Seismic Refraction ◽  
Reykjanes Ridge

scholarly journals Upper-crustal structure beneath the Strait of Georgia, Southwest British Columbia

2007 ◽  
Vol 170 (2) ◽  
pp. 800-812 ◽  
Author(s):  
R. K. Dash ◽  
G. D. Spence ◽  
M. Riedel ◽  
R. D. Hyndman ◽  
T. M. Brocher
Keyword(s):  
British Columbia ◽  
Crustal Structure ◽  
Strait Of Georgia

scholarly journals Crustal deformation and regional metamorphism across a terrane boundary, Coast Plutonic Complex, British Columbia

Tectonics ◽  
1987 ◽  
Vol 6 (3) ◽  
pp. 343-361 ◽  
Author(s):  
M. L. Crawford ◽  
L. S. Hollister ◽  
G. J. Woodsworth
Keyword(s):  
British Columbia ◽  
Crustal Deformation ◽  
Regional Metamorphism ◽  
Plutonic Complex ◽  
Coast Plutonic Complex
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