Lithospheric structure beneath the Archaean Slave Province and Proterozoic Wopmay orogen, northwestern Canada, from a lithoprobe refraction/wide-angle reflection survey

Abstract

SUMMARY The Slave geological province, a relatively small craton in NW Canada that includes the oldest rocks in the world, is one of five cratons that form the Archaean continental core of North America. The Palaeoproterozoic Wopmay orogen, lying between the craton and the Phanerozoic northern Canadian Cordillera, represents crustal growth through addition of a series of north‐south oriented magmatic arcs and accreted terranes. As part of Lithoprobe's multidisciplinary studies, Line 11 of the SNoRE 97 seismic refraction/wide‐angle reflection survey investigated the structure of the lithosphere in this region. Interpretation of crustal and mantle arrivals from 13 record sections followed an iterative procedure of traveltime inversion and forward modelling. Results show that crustal thickness at 32–35 km remains relatively constant from the Archaean regions in the east to Proterozoic domains in the west, contrary to average values of crustal thicknesses from global compilations that suggest thicker Proterozoic crust. At the westernmost end of the line, where crustal extension and basin formation are inferred, the crust thins to 30 km. Upper crustal velocities to about 12 km depth lie in the range of 5.8–6.2 km s−1. The middle crust of thickness 8–10 km has velocities between 6.2 and 6.6 km s−1. Average velocities for the lower crust, differentiated as a 10 km thick layer, range between 6.6 and 6.9 km s−1 with a higher velocity region (7.1 km s−1) in the transition zone between the Fort Simpson magmatic arc and Hottah accreted terrane in the Wopmay orogen, where a Palaeoproterozoic subduction zone has been inferred from coincident multichannel reflection data. In the same area, anomalously low upper‐mantle velocities (7.5 km s−1) have been found, indicating that the effects of collision, subduction and accompanying physical changes in the rocks comprising the mantle lithospheric wedge above the underthrusting structure, may have been retained for 1800 Ma. Data from most record sections with offset distances greater than 250 km show continuous wide‐angle reflections from upper‐mantle depths of about 75 km and almost 100 km. Although poorly constrained, velocities in this depth range vary from 8.4 to 8.8 km s−1. Interpretation of these phases and mantle reflections from equivalent depths in coincident, near‐vertical incidence multichannel data relates them to subduction and underthrusting of oceanic crust and subsequent phase changes that occurred during the assembly of the craton and the evolution of the Palaeoproterozoic orogen.

The teleseismic signature of fossil subduction: Northwestern Canada

“…Wide-angle reflection/refraction data indeed show high crustal and low mantle velocities along this stretch of profile [Fernández-Viejo and Clowes, 2003]. Further study by Fernández-Viejo et al [2005] that combined both P-and S-wave observations yielded additional insights into the nature of the wedge.…”

“…We compare our results with the SNORCLE near-vertical reflection [Cook et al, 1998;Cook and Vasudevan, 2003] and wide-angle reflection/refraction studies [Fernández-Viejo and Clowes, 2003], and teleseismic receiver function analysis from the Yellowknife array [Bostock, 1998]. …”

3-D geomechanical–numerical model of the contemporary crustal stress state in the Alberta Basin (Canada)

“…Coblentz and Richardson, 1996;Dyksterhuis et al, 2005;Humphreys and Coblentz, 2007;Jarosinski et al, 2006), large-scale (regional) models in 3-D (Buchmann and Connolly, 2007;Hergert and Heidbach, 2011;Parsons, 2006), as well as local (reservoir-scale) 3-D models (e.g. Fischer and Henk, 2013;Heidbach et al, 2013;Henk, 2005;Orlic and Wassing, 2012;Van Wees et al, 2003). Modelling of the contemporary stress field mainly depends on the structural model, the material properties, the initial stress state and the applied displacement boundary conditions.…”

“…Usually, there are little in situ stress data available for model calibration in published studies (e.g. Buchmann and Connolly, 2007;Fischer and Henk, 2013;Heidbach et al, 2013;Hergert and Heidbach, 2011), which rules out any statistical validation.…”

“…5) by directional kriging. These are data from seismic refraction studies (Bouzidi et al, 2002;Burianyk et al, 1997;Clowes et al, 2002;Fernández-Viejo and Clowes, 2003;Halchuk and Mereu, 1990;Németh et al, 1996Németh et al, , 2005Spence and McLean, 1998;Welford et al, 2001;Zelt and White, 1995) and from teleseismic studies (Gu et al, 2011;Shragge et al, 2002).…”