Proterozoic craton to basin crustal transition in western Canada and its influence on the evolution of the Cordillera

1991 ◽  
Vol 28 (8) ◽  
pp. 1148-1158 ◽  
Author(s):  
Frederick A. Cook ◽  
John L. Varsek ◽  
Elizabeth A. Clark
Keyword(s):  
Foreland Basin ◽  
Western Canada ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Sufficient Distance ◽  
Thrust Sheets ◽  
Alberta Basin ◽  
Mackenzie Mountains ◽  
Thin Crust

Deep seismic reflection data have imaged a crustal-scale, west-facing ramp or ramp system in the subsurface of western Canada. In northwestern Canada the ramp is within Proterozoic crust east of the Cordillera and is unconformably overlain by Paleozoic sedimentary rocks, indicating that it was formed during the Proterozoic in this region. Similar structures are visible within the Cordillera in southern Canada and the northwestern United States along a south projection of the ramp observed in the north. In the Monashee Complex of British Columbia and in the Priest River Complex in northern Washington, reflections are visible that dip westward from the surface to near the base of the crust and are structurally discordant with underlying more horizontal reflections, thus outlining footwall ramps. We propose that the Proterozoic crustal ramp in the north and the footwall ramps in the Cordillera probably coincide with a Proterozoic crustal transition from thick craton on the east to thin crust on the west. This transition may have influenced sedimentation patterns during deposition of Middle Proterozoic Belt–Purcell and Wernecke strata (ca. 1.6–1.3 Ga) and probably controlled the arcuate shape of the Mackenzie Mountains during their formation in the Mesozoic. This interpretation is consistent with the notion that thrust sheets of the Mackenzie Mountains did not extend onto the craton a sufficient distance to produce flexural subsidence of the thick crust and associated foreland basin development, whereas thrust sheets of the southern Canadian Cordillera were driven eastward and loaded the thick craton, causing crustal flexure and development of the Alberta Basin.

scholarly journals Active strike-slip faults and an outer frontal thrust in the Himalayan foreland basin

2020 ◽  
Vol 117 (30) ◽  
pp. 17615-17621
Author(s):  
Michael J. Duvall ◽  
John W. F. Waldron ◽  
Laurent Godin ◽  
Yani Najman
Keyword(s):  
Foreland Basin ◽  
Historical Seismicity ◽  
Indian Plate ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Triangle Zone ◽  
Blind Thrust ◽  
Thrust Sheets ◽  
Himalayan Foreland Basin ◽  
Basement Ridge

The Himalayan foreland basin formed by flexure of the Indian Plate below the advancing orogen. Motion on major thrusts within the orogen has resulted in damaging historical seismicity, whereas south of the Main Frontal Thrust (MFT), the foreland basin is typically portrayed as undeformed. Using two-dimensional seismic reflection data from eastern Nepal, we present evidence of recent deformation propagating >37 km south of the MFT. A system of tear faults at a high angle to the orogen is spatially localized above the Munger-Saharsa basement ridge. A blind thrust fault is interpreted in the subsurface, above the sub-Cenozoic unconformity, bounded by two tear faults. Deformation zones beneath the Bhadrapur topographic high record an incipient tectonic wedge or triangle zone. The faults record the subsurface propagation of the Main Himalayan Thrust (MHT) into the foreland basin as an outer frontal thrust, and provide a modern snapshot of the development of tectonic wedges and lateral discontinuities preserved in higher thrust sheets of the Himalaya, and in ancient orogens elsewhere. We estimate a cumulative slip of ∼100 m, accumulated in <0.5 Ma, over a minimum slipped area of ∼780 km2. These observations demonstrate that Himalayan ruptures may pass under the present-day trace of the MFT as blind faults inaccessible to trenching, and that paleoseismic studies may underestimate Holocene convergence.

EXTENDED ARRAYS FOR MARINE SEISMIC ACQUISITION

Geophysics ◽  
1978 ◽  
Vol 43 (1) ◽  
pp. 3-22 ◽  
Author(s):  
J. H. Lofthouse ◽  
G. T. Bennett
Keyword(s):  
Data Quality ◽  
Data Acquisition ◽  
Signal Amplitude ◽  
Eastern Canada ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
Formed Part ◽  
Marine Seismic ◽  
Receiver Arrays

In‐line arrays for both source and receiver have been implemented for marine seismic reflection data acquisition. The in‐line array dimensions (variable within limits) are considerably greater than any previously used system of which we are aware. The arrays were designed to attenuate extremely strong sea‐bottom multiples during the data acquisition phase. The source comprised 25 airguns arranged in five identical in‐line subarrays. Each subarray produced a signal of better than 6 barmeters acoustic intensity with a primary‐to‐bubble ratio of approximately 4.4 from guns totaling 297 cu in. When this source was delivered in 1973, it constituted the most powerful production airgun source for which we had seen calibration measurements. Receiver arrays were implemented by a “weighting‐mixing” box (which formed part of the DFS IV instrument), the input to which comprised 53 channels of data each from a 50 m live section in the streamer cable. Processing techniques which are complementary to the field procedures have been developed. Comparisons with “conventional” data (and such data processed to simulate field arrays) show significant improvements in “data quality” from the new field techniques, that is, the new data are easier to interpret geologically because interfering multiples have been attenuated relative to desired energy. Whilst the large outgoing signal amplitude will have made some contribution to the data quality, the major improvement is believed to result from the use of arrays in the recording phase. This system, first used for production in August 1973, was subsequently used successfully during recording of 17,000 km of offshore seismic data from Eastern Canada, the North Sea, and the Mediterranean.

Structural variation along the Devil's Mountain fault zone, northwestern Washington

2006 ◽  
Vol 43 (4) ◽  
pp. 433-446 ◽  
Author(s):  
Nathan Hayward ◽  
Mladen R Nedimović ◽  
Matthew Cleary ◽  
Andrew J Calvert
Keyword(s):  
Fault Zone ◽  
Structural Variation ◽  
Puget Sound ◽  
Seismic Reflection Data ◽  
Juan De Fuca Plate ◽  
The North ◽  
Reflection Data ◽  
Juan De Fuca ◽  
Main Fault ◽  
Juan De Fuca Strait

The eastern Juan de Fuca Strait is subject to long-term, north–south-oriented shortening. The observed deformation is interpreted to result from the northward motion of the Oregon block, which is being driven north by oblique subduction of the oceanic Juan de Fuca plate. Seismic data, acquired during the Seismic Hazards Investigation in Puget Sound survey are used, with coincident first-arrival tomographic velocities, to interpret structural variation along the Devil's Mountain fault zone in the eastern Juan de Fuca Strait. The Primary fault of the Devil's Mountain fault zone developed at the northern boundary of the Everett basin, during north–south-oriented Tertiary compression. Interpretation of seismic reflection data suggests that, based on their similar geometry including the large magnitude of pre-Tertiary basement offset, the Primary fault of the Devil's Mountain fault west of ~122.95°W and the Utsalady Point fault represent the main fault of the Tertiary Devil's Mountain fault zone. The Tertiary Primary fault west of ~122.95°W was probably kinematically linked to faults to the east (Utsalady Point, Devil's Mountain, and another to the south), by an oblique north–northeast-trending transfer zone or ramp. Left-lateral transpression controlled the Quaternary evolution of the Devil's Mountain fault zone. Quaternary Primary fault offsets are smaller to the east of ~122.95°W, suggesting that stress here was in part accommodated by the prevalent oblique compressional structures to the north. Holocene deformation has focussed on the Devil's Mountain, Utsalady Point, and Strawberry Point faults to the east of ~122.8° but has not affected the Utsalady Point fault to the west of ~122.8°W.

Seismic evidence for the migration of fluids within the accretionary complex of western Canada

1991 ◽  
Vol 28 (4) ◽  
pp. 542-556 ◽  
Author(s):  
A. J. Calvert ◽  
R. M. Clowes
Keyword(s):  
Continental Slope ◽  
Seismic Data ◽  
Accretionary Prism ◽  
Western Canada ◽  
Accretionary Wedge ◽  
Seismic Velocities ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Subducting Plate ◽  
Important Evidence

Multichannel deep seismic reflection data from the subduction zone of western Canada delineate the wedge of accereted sediments and the principal terranes (Crescent, Pacific Rim, and Wrangellia) that form the convergent margin. The top of the igneous oceanic crust is defined by subhorizontal reflections extending at least 100 km landward of the deformation front. Upon incorporation into the accretionary wedge, the clearly defined stratigraphy of the incoming oceanic sedimentary section is destroyed over a distance of about 10 km. Initially, an unreflective zone, which correlates well with maximum fluid expulsion, is formed. Farther landward, a predominantly landward-dipping reflectivity exists. A number of reflections are thrust faults, which appear to merge at depth with the subhorizontal reflections, but most have another origin. These reflections may be related to the movement of fluids generated by the compaction of sediments or possibly by the dehydration of the subducting plate. They are strongest in a region of depressed seismic velocities beneath the continental slope, where an analysis of reflection amplitude with offset implies that a high Poisson's ratio exists; this is consistent with the presence of elevated pore pressures. Thus, pore pressure variations associated with the migration of fluids may be the cause of much of the reflectivity within the accreted wedge, although the precipitation of minerals from rising fluids could also be important. Evidence from the seismic data also indicates that fluids from the accretionary prism are being expelled into the sediments of the overlying Tofino basin. A number of anomalously strong reflections and disruption of the horizontally stratified sediments within the lower levels of the basin probably represent fluids that migrated upward from the accreted wedge and were trapped against impermeable barriers created through the deposition of sediments on the continental slope and in the basin.

scholarly journals Sevier Fault at Red Canyon

Geosites ◽  
2019 ◽  
Vol 1 ◽  
pp. 1-6
Author(s):  
Robert Biek
Keyword(s):  
Lava Flow ◽  
Fault Zone ◽  
Hanging Wall ◽  
Slip Rate ◽  
Normal Fault ◽  
Coarse Grained ◽  
Seismic Reflection Data ◽  
The North ◽  
Total Displacement ◽  
Reflection Data

The Sevier fault is spectacularly displayed on the north side of Utah Highway 12 at the entrance to Red Canyon, where it offsets a 500,000-year-old basaltic lava flow. The fault is one of several active, major faults that break apart the western margin of the Colorado Plateau in southwestern Utah. The Sevier fault is a “normal” fault, a type of fault that forms during extension of the earth’s crust, where one side of the fault moves down relative to the other side. In this case, the down-dropped side (the hanging wall) is west of the fault; the upthrown side (the footwall) lies to the east. The contrasting colors of rocks across the fault make the fault stand out in vivid detail. Immediately south of Red Canyon, the 5-million-year-old Rock Canyon lava flow, which erupted on the eastern slope of the Markagunt Plateau, flowed eastward and crossed the fault (which at the time juxtaposed non-resistant fan alluvium against coarse-grained volcaniclastic deposits) (Biek and others, 2015). The flow is now offset 775 to 1130 feet (235-345 m) along the main strand of the fault, yielding an anomalously low vertical slip rate of about 0.05 mm/yr (Lund and others, 2008). However, this eastern branch of the Sevier fault accounts for only part of the total displacement on the fault zone. A concealed, down-to-the-west fault is present west of coarse-grained volcaniclastic strata at the base of the Claron cliffs. Seismic reflection data indicate that the total displacement on the fault zone in this area is about 3000 feet (900 m) (Lundin, 1987, 1989; Davis, 1999).

Rift processes in the Westralian Superbasin, North West Shelf, Australia: insights from 2D deep reflection seismic interpretation and potential fields modelling

2015 ◽  
Vol 55 (2) ◽  
pp. 400 ◽  
Author(s):  
Catherine Belgarde ◽  
Gianreto Manatschal ◽  
Nick Kusznir ◽  
Sonia Scarselli ◽  
Michal Ruder
Keyword(s):  
Seismic Reflection ◽  
Potential Fields ◽  
Moho Depth ◽  
Late Permian ◽  
Forward Modelling ◽  
Seismic Reflection Data ◽  
North West ◽  
Reflection Seismic ◽  
The North ◽  
Reflection Data

Acquisition of long-offset (8–10 km), long-record length (12–18 sec), 2D reflection seismic and ship-borne potential fields data (WestraliaSpan by Ion/GXT and New Dawn by PGS) on the North West Shelf of Australia provide the opportunity to study rift processes in the context of modern models for rifted margins (Manatschal, 2004). Basement and Moho surfaces were interpreted on seismic reflection data. Refraction models from Geoscience Australia constrain Moho depth and initial densities for gravity modelling through standard velocity-density transformation. 2D joint inversion of seismic reflection and gravity data for Moho depth and basement density constrain depth to basement on seismic. 2D gravity and magnetic intensity forward modelling of key seismic lines constrain basement thickness, type and density. Late Permian and Jurassic-Early Cretaceous rift zones were mapped on seismic reflection data and constrained further by inversion and forward modelling of potential fields data. The Westralian Superbasin formed as a marginal basin in Eastern Gondwana during the Late Permian rifting of the Sibumasu terrane. Crustal necking was localised along mechanically-weak Proterozoic suture belts or Early Paleozoic sedimentary basins (such as Paterson and Canning). Mechanically-strong cratons (such as Pilbara and Kimberley) remained intact, resulting in necking and hyper-extension at their edges. Late Permian hyper-extended areas (such as Exmouth Plateau) behaved as mechanically-strong blocks during the Jurassic to Early Cretaceous continental break-up. Late Permian necking zones were reactivated as failed-rift basins and localised the deposition of the Jurassic oil-prone source rocks that have generated much of the oil discovered on the North West Shelf.

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