The electrical resistivity of Canada’s lithosphere and correlation with other parameters: contributions from Lithoprobe and other programmes

Abstract

Over the last 30 years, through Lithoprobe and other programmes, modern, high-quality magnetotelluric (MT) measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across Canada in all provinces and territories, except Nova Scotia. Some regions are well covered, particularly Alberta, southern British Columbia, and western Ontario, whereas others remain poorly covered, such as Quebec and large swaths of Nunavut. Prior publications from individual studies have added significantly to the wealth of Canada’s geoscience knowledge, and have demonstrated that MT can contribute significantly to understanding of the tectonic processes that have shaped Canada. However, to date no continent-scale maps of lithospheric electrical parameters have been constructed from the extensive MT database. Herein we review the contributions made by the MT components of Lithoprobe, and present new continental-scale maps of various electrical parameters at crustal and upper mantle depths for the whole of Canada. From those maps, combined with regional estimates of temperature, we develop derivative information on petrological–geophysical properties, including predictions of temperature and water content. We find that at 100 km depth the Canadian Shield is cold and dry, and the Cordillera is warmer but mostly dry, i.e., little water is present in the peridotite. Exceptions are beneath the Prairies, the Wopmay Orogen, and northeast Nunavut where there does appear to be water in the nominally anhydrous minerals. Also, southwest British Columbia appears colder than the rest of the Cordillera due to the subducting Juan de Fuca plate. In contrast, at 200 km depth almost all of Canada is dry.