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 associated with the assembly of Laurentia and subsequent kimberlite magmatism. The depth of the lithosphere–asthenosphere boundary across Alberta varies from 150 to 300 km as defined from the 100 Ω m 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.