Three-dimensional crustal and upper-mantle resistivity structure of Alberta, Canada: implications for Precambrian tectonics

Abstract

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.

The Relationship Between Kimberlitic Magmatism and Electrical Conductivity Anomalies in the Mantle

“…Kimberlites also tend to avoid strong conductors (e.g., beneath the Bushveld Complex) and highly resistive lithospheric columns (e.g., the resistive keel of the Kaapvaal Craton). Similar relationships between conductors and kimberlites have also been observed in previous studies (e.g., Bettac, 2020; Jones et al., 2003, 2005; Wang & Unsworth, 2022). Here, we analyze data from major global kimberlite provinces that are imaged with high‐quality MT to understand the relationship between kimberlite emplacement, diamond formation/survival, and electrical conductivity anomalies.…”

“…We investigate MT models from southern Africa (Özaydın et al., 2022), north‐central USA (Bedrosian & Finn, 2021), eastern USA (Kelbert et al., 2019), the Slave Craton (Bettac, 2020), Alberta basement (Wang & Unsworth, 2022), the Rae Craton (Spratt et al., 2014), the Alto Paranaiba Province in Brazil (Bologna et al., 2006), and the Delamerian Orogen and Gawler Craton in South Australia (Robertson et al., 2021). Five datasets are analyzed directly from a 3D model (Figures 2a–2e), while the others were digitized at the kimberlite localities and analyzed as profiles (Figures S6–S45 in Supporting Information ).…”

Modeling Geomagnetically Induced Currents in the Alberta Power Network: Comparison and Validation Using Hall Probe Measurements During a Magnetic Storm

“…It is also worth noting that the data-space modeling method yielded better results than the model-space modeling method only at Ellerslie although the peak values still did not exceed 70 A (see Supporting Information S1). This may suggest a unique influence of Earth conductivity in the vicinity of Ellerslie substation given its proximity to a lower crustal conductor previously noted to have an influence on (Cordell et al, 2021;Wang & Unsworth, 2022). However, given these results, tests, and considerations, it is still unclear how over two times the current could be flowing to ground at Ellerslie without significantly altering the overall current flows in the network model, and thus degrading the data fits at other nearby substations such as Sunnybrook and Keephills.…”

“…Alberta is unique due to a wealth of data relevant to GICs including a relatively dense network of magnetic stations as part of the Canadian Array for Realtime Investigations of Magnetic Activity (CARISMA) which enables the characterization of meso‐scale magnetic activity, such as perturbations associated with sub‐storm activity (Mann et al., 2008). In addition, there is also a dense array of more than 500 surface impedance measurements collected using the MT method previously used for geological applications (Figure 1; Cordell et al., 2021; Wang & Unsworth, 2022). Recently, AltaLink—one of the largest power transmission companies in the province—installed Hall effect GIC monitoring devices at five substation transformer neutrals (Figure 1), providing a key data stream to compare with modeled GICs.…”