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.

The Jinshajiang-Ailaoshan alkaline porphyry Cu, Mu, and Au polymetallic belt is an important Cenozoic metallogenic belt in SW China which extends for over 1,000 km (Figure 1a; W. C. . It is adjacent to the intra-continental Jinshajiang-Red River strike-slip fault system of the Tethys-Himalaya orogenic belt. This belt hosts dozens of economically significant porphyry and skarn ore deposits that are related to potassic porphyritic intrusions (Hou et al., 2017). It is believed to be the result of the long-term interaction between the Indochina and the Yangtze craton and the lateral extrusion of the Indochina block during the continental collisional process of the Tibet and the Indian block (Deng et al., 2015).

Summary This paper describes the first detailed 3-D study of the Alberta basement using the magnetotelluric (MT) method. Long-period MT data were used to generate a 3-D electrical resistivity model of the crust and upper mantle beneath Alberta. The Western Canada Sedimentary Basin was imaged as a low resistivity layer. A number of crustal and upper mantle conductors were imaged and include: (1) the Red Deer conductor, (2) the Kiskatinaw conductor, (3) a conductor coincident with the Kimiwan oxygen isotope anomaly, (4) the southern Alberta—British Columbia conductor, (5) the Loverna block conductor, and (6) a conductor beneath the Birch Mountain kimberlite field. Conductors (3) and (6) are newly identified in this study. All of these conductors can be related to past tectonic events associate with the assembly of Laurentia and subsequent kimberlite magmatism. The depth of the lithosphere-asthenosphere boundary across Alberta varies from 150 km to 300 km as defined from the 100 Ωm contour. Furthermore, the Snowbird tectonic zone in Alberta is characterized by a thick, resistive lithosphere.  Similarly, the diamondiferous Buffalo Head Hills kimberlite field is imaged with a thick, resistive lithosphere, both may indicate depletion. In contrast, the Birch Mountain kimberlite field is underlain by a pronounced conductor that extends through the lithosphere and may be the result of metasomatism.