Moho Variations across the Northern Canadian Cordillera

Abstract

Moho morphology in orogens provides important constraints on the rheology and density structure of the crust and underlying mantle. Previous studies of Moho geometry in the northern Canadian Cordillera (NCC) using very sparse seismic data have indicated a flat and shallow (∼30–35 km) Moho, despite an average elevation of >1000 m above sea level attributable to increased thermal buoyancy and lower crustal flow due to elevated temperatures. We estimate Moho depth using receiver functions from an expanded dataset incorporating 173 past and recently deployed broadband seismic stations, including the EarthScope Transportable Array, Mackenzie Mountains transect, and other recent deployments. We determine Moho depths in the range 27–43 km, with mean and standard deviations of 33.0 and 3.0 km, respectively, and note thickened crust beneath high-elevation seismogenic regions. In the Mackenzie Mountains, thicker crust is interpreted as due to crustal stacking from thrust sheet emplacement. The edge of this region of thickened crust is interpreted to delineate the extent of the former Laurentian margin beneath the NCC and is associated with a transition from thrust to strike-slip faulting observed in regional seismicity. More geographically extensive seismograph deployments at EarthScope Transportable Array density and scale will be required to further extend crustal-scale and lithosphere-scale imaging in western Canada.

Geophysical reassessment of the role of ancient lineaments on the development of the western Laurentian margin and its sediment-hosted Zn–Pb deposits, Yukon and Northwest Territories, Canada

“…8a). Audet et al (2020) suggest that the Moho broadly deepens towards the southeast in the vicinity of the FNS, but a direct relationship cannot be confirmed due to the presently low seismic station coverage in this region.…”

“…7b), a southeastward deepening of the Moho (Fig. 9, Welford et al 2001;Clowes et al 2005;Audet et al 2020) with an associated increase in seismic velocity (Estève et al 2020), and a change in the orientation of the seismic anisotropy (Courtier et al 2010).…”

“…Figure 9 shows that following palinspastic restoration, many MVT Zn-Pb occurrences straddle or lie southwest of the NW-trending lineament aligned with the Richardson-Hess fault system. Mississippi Valley-type mineral occurrences are spatially associated with a region where the Moho and LAB shallow toward the southwest (Audet et al 2020;Hoggard et al 2020). Many MVT Zn-Pb occurrences are also located on the margin of the Misty Creek Embayment, now aligned with the Richardson Trough.…”

“…7b). Seismic models (Audet et al 2020) show a broad increase in bulk crustal V p /V s ratio from south to north (~1.72 to 1.82) across the feature. High-density sources beneath the northern Mackenzie Mountains, immediately south of the Cordilleran deformation front trend ENE in alignment with both the edge of the MRA (Fig.…”

“…Passive seismic techniques also provide information on regional variations in Moho depth and bulk crustal composition (e.g., Courtier et al 2010;Audet et al 2020) and can thus provide information on crustal domains and boundaries.…”