Geoelectric structure of the Great Slave Lake shear zone in northwest Alberta: implications for structure and tectonic history

Abstract

The study of ancient plate boundaries can provide insights into the past and present-day tectonic processes. Here, we describe a magnetotellurics (MT) study of the Precambrian basement of the Hay River Fault (HRF) in northwest Alberta, which is the southwest segment of the Great Slave Lake shear zone. New broadband MT data were collected to give a clearer image of the crustal structure. The Western Canada Sedimentary Basin was imaged as a low-resistivity layer above the resistive crystalline basement. Four basement conductors were defined, and correlate with the terrane boundaries delineated with aeromagnetic data. These are (1) a major conductor in the Kiskatinaw domain, (2) a conductor on the boundary of the Ksituan and Chinchaga domains, (3) a conductor on the boundary of the Chinchaga and Buffalo Head domains, and (4) a conductor near the HRF. Both (1) and (2) correspond to areas of high seismic reflectivity. The low resistivity can be explained by interconnected grain boundary graphite or sulfide phases deposited by metamorphic fluid migration. The HRF was not definitively located in previous studies. The new data show that the HRF could be thin (1 km) or wide (10 km) and located at the boundary of the contrasting aeromagnetic anomalies or further to the north. Various tectonic processes are proposed to interpret the possible locations of the HRF. No electrical anisotropy structure is required to interpret the MT data in this study.

Estimating the Geoelectric Field and Electric Power Transmission Line Voltage During a Geomagnetic Storm in Alberta, Canada Using Measured Magnetotelluric Impedance Data: The Influence of Three‐Dimensional Electrical Structures in the Lithosphere

“…In Alberta and southeastern British Columbia, a large regional array of long-period MT data has been collected at 530 locations using 10-20 km average site spacing south of 55°N and sparser coverage to the north (Figure 1b; Hanneson et al, 2021;Wang, 2019). The MT method is a well-established geophysical exploration method and parts of this array have previously been used to study the geology of Western Canada in the search for hydrocarbon, mineral and geothermal resources (Hanneson et al, 2021;Liddell et al, 2016;Nieuwenhuis et al, 2014;Wang et al, 2018;Xiao & Unsworth, 2006). MT data were collected using several types of instruments.…”

New Insights Into Crustal and Mantle Flow Beneath the Red River Fault Zone and Adjacent Areas on the Southern Margin of the Tibetan Plateau Revealed by a 3‐D Magnetotelluric Study

“…Deformation in strike-slip faults at such depths will have been ductile owing to the high pressures and temperatures. While this can result in low resistivity when active, it could led to high resistivity when the shear zone becomes inactive and cools down (Wang et al, 2018). Examples of this pattern have been reported from the Great Slave Lake Shear Zone (GSLSZ) and the Tintina Fault (Ledo et al, 2002) in Canada.…”

Evidence for Post‐Assembly Modification of Western Laurentia by Back‐Arc Extension

“…It has been postulated to have formed during Paleoproterozoic convergence of the Slave and Rae provinces (Hoffman, 1988; D. I. Pana, 2003). To the southwest, a buried subsurface extension of the GSLSZ with slightly younger displacement is identified as the Hay River Fault (HRF; E. Wang, Unsworth, & Chacko, 2018). Exhumed mylonites within the GSLSZ record deformation at mid‐crustal depth (Dyck et al., 2021), while the HRF documents a later phase of brittle faulting (Hanmer et al., 1992).…”

“…Geophysical studies in western Laurentia include aeromagnetic, gravity, geothermic, and magnetotelluric investigations (Boerner et al., 2000; Pilkington et al., 2000; E. Wang, Unsworth, & Chacko, 2018) as well as crustal‐scale seismic‐reflection and refraction profiles (e.g., Ross & Eaton, 2002; Zelt & Ellis, 1989). In this study, we focus on potential‐field and seismic‐reflection profiles.…”

“…Laurentia, the cratonic core of the North American continent, was assembled ca. 2.1‐1.8 Ga into its present configuration of lithospheric domains (Bao & Eaton, 2015; Hoffman, 1988; Hoffman et al., 1989; Ross & Eaton, 2002; E. Wang et al., 2018; Whitmeyer & Karlstrom, 2007). Past studies of the lithospheric architecture of Laurentia have focused primarily on collisional assembly, with relatively little attention given to processes of syn‐ and post‐assembly lithospheric modification ‐ although these processes are commonly observed in modern tectonic settings.…”