Seismic anisotropy associated with continental lithosphere accretion beneath the CANOE array, northwestern Canada

Courtier, A. M.; Gaherty, J. B.; Revenaugh, J.; Bostock, M. G.; Garnero, Edward J.

doi:10.1130/g31120.1

Cited by 30 publications

(34 citation statements)

References 24 publications

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“…Anisotropy has also been cited as a possible mechanism of LVZs [ Zorin et al , ] since the reorientation of minerals under regional stress field could reduce the seismic velocity along certain orientations. Earlier studies of seismic anisotropy have suggested dominant (fast) orientations of 33–43° in the mantle (Figure a) [ Shragge et al , ; Courtier et al , ] beneath Alberta. These values are in rough alignment with the present‐day plate motion (see Figure a).…”

Section: Discussionmentioning

confidence: 99%

Crustal imprints of Precambrian orogenesis in western Laurentia

Chen

Dokht

et al. 2015

JGR Solid Earth

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Crustal low‐velocity zones (LVZs) have been reported in active orogens such as the Himalayas and the Andes but rarely in stable cratonic regions. In this study, we provide compelling evidence for a significant midcrustal LVZ beneath eastern‐central Alberta, an integral part of the Precambrian Canadian Shield covered by thick Phanerozoic sedimentary deposits. This 200 km wide, over 10 km thick midcrustal LVZ is well resolved by shear velocity inversions using P‐to‐S receiver functions from more than 4600 earthquakes. It is generally overlain by a high‐velocity upper crust in the depth range of 8–15 km, especially in western‐central Alberta, which coincides with the previously documented Winagami reflection sequence. We interpret the LVZ to be of granitic composition, potentially in connection with the crystallization of partially molten crust during the Paleoproterozoic eon. In addition to the Precambrian tectonic history of western Laurentia, which featured plate convergence conducive to crustal melting, our crustal model is further supported by (1) a moderate spatial correlation between the LVZ and heat flow, and (2) shear velocities consistent with that of granite. The well preserved Winagami reflection sequence and the LVZ are potential evidence of distinct episodes of magmatism and crust modification in the Precambrian basement of the Western Canada Sedimentary Basin. The existence of a broad crustal LVZ suggests extensive subduction, orogenesis, and crustal melting during the Precambrian assembly of the North American craton.

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Section: Discussionmentioning

confidence: 99%

Crustal imprints of Precambrian orogenesis in western Laurentia

Chen

Dokht

et al. 2015

JGR Solid Earth

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“…The western edge of the sedimentary basin is demarcated by the Canadian Rockies, a part of the Western Cordillera likely formed in the late Cretaceous and early Tertiary during the Laramide orogeny (Livaccari et al 1981;Maxson and Tickoff 1996;English and Johnson 2004;Cook et al 2010;Liu et al 2010). While regionally deep Moho interfaces have been observed and interpreted as the isostatic response to loading of the lithosphere by Mesozoic thrust sheets (e.g., Price 1981;Cook 1995Cook , 2002, the cause of the Laramide phase of mountain building and its effect on crust/lithosphere thickness remains uncertain (English and Johnson 2004;Liu et al 2010) Evidence from regional gravity, magnetic, and seismic surveys (see Ross 2000 and references therein; van der Lee and Frederiksen 2005; Marone and Romanowicz 2007;Courtier et al 2010;Yuan and Romanowicz 2010) suggests the presence of major seismic velocity gradients and shear wave anisotropy beneath a broad spectrum of tectonic domains (e.g., Buffalo Head, Wabamum, Thorsby, Lacombe, Eyehill, and Loverna; Hoffman 1988; Ross et al 2000;Clowes et al 2002) (see Figure 5). The age and origin of these domains and the extent of tectonic overprinting (e.g., Ross and Eaton 2002) remains questionable.…”

Section: Tectonic Setup and Motivationmentioning

confidence: 98%

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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“…Among the best-resolved regions, the most robust conversions from the 520 are observed in southern Alberta Basin, especially at stations CLA and WALA. Increased conversion amplitudes could result from reduced sharpness due to the presence of fluid, as documented by Courtier et al [2006] in eastern U.S., though better station and data coverage than that available to this study will be necessary to verify this result. The simplicity of the 520 is supported by Schmandt et al [2012], though the amplitude and depth of the 520 are considerably larger than those of the earlier study.…”

Section: 1002/2014jb011802mentioning

confidence: 94%

“…In view of the Mesozoic tectonic history of North America, this high-velocity signature may be caused by the remnant of the subducted Farallon/Kula Plate. In fact, earlier studies based on different data types [Bostock, 1996;Melbourne and Helmberger, 2002;Courtier et al, 2006;Schmandt et al, 2012] have revealed fragments of Mesozoic slabs in various parts of the North American continent. Residual thermal anomaly from subduction could account for a local temperature difference of 400°C [Schmid et al, 2002].…”

Section: Mtz Thicknessmentioning

confidence: 99%

“…While global discontinuity maps [e.g., Flanagan and Shearer, 1998;Gu et al, 2003;Lawrence and Shearer, 2008] suggest a relatively flat MTZ, diminished discontinuity topography could be partially attributable to the averaging effects of large Fresnel zones [Neele et al, 1997]. The use of higher-resolution approaches such as receiver functions was previously limited to sparsely populated national network stations [Cassidy, 1995;Bostock, 1996], linear temporary arrays [Shragge et al, 2002;Courtier et al, 2006], or crustal-scale investigations [Clowes et al, 2002;Bostock et al, 2010;Cassidy, 1995].…”

Section: General Assessmentmentioning

confidence: 99%

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Sharp mantle transition from cratons to Cordillera in southwestern Canada

Zhang

Sacchi

et al. 2015

JGR Solid Earth

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The Western Canada Sedimentary Basin marks the transition from the old North American continental lithosphere to young accreted terranes. Earlier studies in this region have suggested a large number of intricate basement domains as well as major seismic velocity gradients in the mantle. To investigate the effect of the accretion and subduction on the mantle structure beneath the western margin of the North American Craton, we analyze P-to-S converted waves from upper mantle discontinuities from the Canadian Rockies and Alberta Network, a regional broadband seismic array based in Alberta, Canada. The depths of the 410 and 660 km seismic discontinuities are correlated and, on average, are 9 km and 7 km greater than their respective global estimates. The largest depression is observed beneath the Rocky Mountain foreland belt in southern Alberta, which highlights a steep southward/westward structural gradient from the cratons to Cordillera at lithospheric mantle depths. The severity of the depressions, especially in the southernmost Alberta, may be triggered by diffuse partial melt or increased water content above the 410 km discontinuity. This result is corroborated by locally increased impedance contrast across the 410 km discontinuity and a strongly depressed 660 km discontinuity. A relic Mesozoic slab fragment may be partially responsible for the deep olivine phase boundary at the base of the upper mantle.

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Seismic anisotropy associated with continental lithosphere accretion beneath the CANOE array, northwestern Canada

Cited by 30 publications

References 24 publications

Crustal imprints of Precambrian orogenesis in western Laurentia

Crustal imprints of Precambrian orogenesis in western Laurentia

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

Sharp mantle transition from cratons to Cordillera in southwestern Canada

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