Body-wave tomography of western Canada

Mercier, Jean-Philippe; Bostock, M. G.; Cassidy, John F.; Dueker, K. G.; Gaherty, J. B.; Garnero, Edward J.; Revenaugh, J.; Zandt, G.

doi:10.1016/j.tecto.2009.05.030

Cited by 56 publications

(63 citation statements)

References 65 publications

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“…Paths that travel fast at short periods and slowly at long periods (colored blue) tend to be located to the northwest of paths that travel slowly at short periods and faster at long periods (colored green), especially for the Rayleigh waves. Upper mantle models of the study area suggest lower wave speeds to the west and higher velocities to the east [Frederiksen et al, 2001;Mercier et al, 2009]. The geographical division of paths that are slow (red and blue) or fast (green and black) at long periods in the west and east, respectively, is consistent with the existence of a similar boundary in the middle and lower crust.…”

Section: Group Velocity Measurementssupporting

confidence: 68%

CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

Dalton¹,

Gaherty²,

Courtier³

2011

J. Geophys. Res.

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Crustal seismic velocity structure in northwest Canada is imaged using group velocity measurements derived from ambient noise cross correlations. The focus area surrounds the Canadian Northwest Experiment (CANOE) array, a 16 month deployment of 59 broadband seismic stations. The CANOE array extended from the Northern Cordillera on the west into the Archean Slave province to the east, crossing crustal terranes that span ∼4 Gyr of Earth history. Forty broadband stations from the Canadian National Seismograph Network and the POLARIS network are also included. The Green's function for each pair of stations is estimated by cross‐correlating 24 h long time series of ambient noise for each day in the time period July 2004 to June 2005. Fundamental mode Rayleigh waves are observed on cross‐correlated vertical component records and Love waves on the transverse components. The group velocity measurements are inverted for 3‐D shear wave velocity within the crust. Local sensitivity kernels are used to account for the effects of a laterally variable sedimentary layer at shallow depths, and receiver function P‐s differential times at the CANOE stations constrain total crustal thickness. Known sedimentary basins dominate lateral variations in wave speed in the shallow crust. In the middle crust, the model contains a strong low‐velocity region that correlates spatially with the location of Proterozoic metasedimentary rocks that have been inferred from active source reflection profiles to occupy much of the crust beneath the Cordilleran terranes. Velocity variations in the lower crust, which are weakly resolved due to the limited period range of our data set (5–20 s), suggest a west‐to‐east transition from lower to higher wave speeds that aligns with the Cordilleran deformation front in parts of the study area. The results presented here are consistent with but do not confirm the notion of Proterozoic strata throughout much of the Cordilleran crust. These metasedimentary rocks, if present, must have experienced some deformation and metamorphism in order to also be consistent with upper mantle seismic models that contain a sharp transition from low to high velocity across the deformation front.

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Section: Group Velocity Measurementssupporting

confidence: 68%

CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

Dalton¹,

Gaherty²,

Courtier³

2011

J. Geophys. Res.

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“…Among them, the anomaly beneath station SLEB (labeled "1" in Figure 14) extends well below mid-crust, as suggested both by Figure 14B and by frequencies lower than 0.03 Hz (not shown). Geographically, this structure resides directly west of the proposed Cordilleran deformation front by Mercier et al (2009) and supports a sharp transition from fast (east of the boundary) to slow (west of the boundary) lower-crust and upper-mantle wave speeds. Unfortunately, a direct comparison of velocities is not possible due to a visible gap in data coverage in Mercier et al (2009).…”

Section: Ambient Noise Group Velocitiessupporting

confidence: 54%

The Canadian Rockies and Alberta Network (CRANE): New Constraints on the Rockies and Western Canada Sedimentary Basin

Okeler

Shen

et al. 2011

Seismological Research Letters

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The Canadian Rockies and the neighboring Alberta Basin mark the transition from the old North American continental lithosphere (east) to young accreted "terranes" (west). Geologic, seismic, and magnetic data in this region have suggested complex crustal domains, conductive anomalies, and major seismic velocity gradients in the mantle. However, the nature of the boundaries between the basement domains and their vertical extents remains controversial due to the lack of exposed geology and limited seismic and electromagnetic receivers. Since 2006, the seismic data coverage and depth sensitivity have received a major boost from the establishment of the Canadian Rockies and Alberta Network (nicknamed CRANE), the first semi-permanent broadband seismic array in Alberta. The availability of the array data provides vital constraints on the regional micro-earthquakes and crust/mantle seismic structures. Among the broad range of ongoing efforts, this study highlights promising results from the analyses of P-to-S wave receiver functions, shear wave splitting amplitudes/directions, and ambient seismic noise. Our preliminary receiver-function stacks show that the base of the crust gradually shallows from approximately 60 km beneath the Rockies near the Canadian-U.S. border to 37-40 km beneath central Alberta; the latter range is consistent with earlier findings from active-source experiments. Converted waves from "littered" crust and/ or lithosphere have also been detected at a number of stations in the depth range of 80-130 km. Complexities in the lithosphere are further evidenced by our regional shear wave splitting measurements. We infer a strong east-west change of mantle flow pattern, consistent with present-day plate motion. The spatial distribution of the SKS fast orientations highlights the contrasting crust/mantle structures and histories between the Rockies and adjacent domains. Dynamic effects associated with a migrating continental root east of the province may be important. Finally, our preliminary inversions using ambient seismic noise indicate more than 0.8 km/s in peak-to-peak group velocity variations throughout the crust. The upper crust beneath the Alberta Basin is dominated by low Rayleigh-wave group velocities. A lower-than-expected correlation between seismic velocities and tectonic domain boundaries suggests significant tectonic overprinting in the southern Western Canada Sedimentary Basin. Overall, the broadband seismic data from CRANE could play a key role in uncovering the mysteries of the crust and mantle beneath the transition region between cratons and terranes.

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“…Explaining the underlying mantle high-velocity zone, however, is problematic for most of these scenarios. This high-velocity feature is not explained, for example, by edge-driven convection alone 9 , and it is unlikely that it represents the Juan de Fuca slab, which has a significantly steeper dip 24 . On the other hand, lithospheric delamination provides a satisfactory explanation for all of our observations, including: history of regional uplift and magmatism; flat Moho 25 ; and shallow asthenosphere underlain by a high-velocity layer, which in this scenario may be interpreted as a foundering block of detached lithosphere.…”

mentioning

confidence: 91%

Plateau uplift in western Canada caused by lithospheric delamination along a craton edge

2014

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Continental plateaux, such as the Tibetan Plateau in Asia and the Altiplano-Puna Plateau in South America, are thought to form partly because upwelling, hot asthenospheric mantle replaces some of the denser, lower lithosphere 1-4 , making the region more buoyant. The spatial and temporal scales of this process are debated, with proposed mechanisms ranging from delamination of fragments to that of the entire lithosphere 1-4 . The Canadian Cordillera is an exhumed ancient plateau that abuts the North American Craton 5 . The region experienced rapid uplift during the mid-to-late Eocene, followed by voluminous magmatism 6 , a transition from a compressional to extensional tectonic regime 7 and removal of mafic lower crust 8 . Here we use Rayleigh-wave tomographic and thermochronological data to show that these features can be explained by delamination of the entire lithosphere beneath the Canadian Cordillera. We show that the transition from the North American Craton to the plateau is marked by an abrupt reduction in lithospheric thickness by more than 150 km and that asthenosphere directly underlies the crust beneath the plateau region. We identify a 250-km-wide seismic anomaly about 150-250 km beneath the plateau that we interpret as a block of intact, delaminated lithosphere. We suggest that mantle material upwelling along the sharp craton edge 9 triggered large-scale delamination of the lithosphere about 55 million years ago, and caused the plateau to uplift.Orogenic plateaux are broad, high-standing, low-relief regions that develop in mature continental mountain belts. Plateaux are important because they affect climate 2 , orogenesis 3 and tectonic plate interactions 10 . Modern examples include the Tibetan Plateau and the Altiplano, which developed in the Cenozoic by some combination of lithospheric delamination, lower crustal flow and regional shortening 1-4 . Although the rates, timing and mechanisms driving plateau uplift remain controversial, lithospheric delamination continues to be a leading mechanism explaining their formation and maintenance, albeit with debated temporal and spatial scales 1-4 .Fossil plateaux can provide important insights into orogenic processes. In the Eocene, the interior of the Canadian Cordillera was perhaps the highest-standing mountain belt on Earth 11 and, in terms of crustal architecture, is one of the best-studied recent orogens. In this region, thickened crust that developed during orogenesis is no longer present 12 ; rather, present-day mountainous topography reflects the isostatic response to regional thermal structure 5 .In this study, we integrate published thermochronology results with new high-resolution teleseismic tomography. We use fundamental-mode Rayleigh waves recorded during the period 2006-2013 at 86 broadband seismograph stations to construct a new three-dimensional tomographic shear-velocity (V s ) model to depths of ∼300 km. Figure 1a shows V s at 105 km depth extracted from our tomographic model, highlighting an abrupt transition from the high-velocity mant...

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Body-wave tomography of western Canada

Cited by 56 publications

References 65 publications

CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

The Canadian Rockies and Alberta Network (CRANE): New Constraints on the Rockies and Western Canada Sedimentary Basin

Plateau uplift in western Canada caused by lithospheric delamination along a craton edge

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Body-wave tomography of western Canada

Cited by 56 publications

References 65 publications

CrustalVSstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

CrustalVSstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

The Canadian Rockies and Alberta Network (CRANE): New Constraints on the Rockies and Western Canada Sedimentary Basin

Plateau uplift in western Canada caused by lithospheric delamination along a craton edge

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CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography

CrustalV_Sstructure in northwestern Canada: Imaging the Cordillera-craton transition with ambient noise tomography