Potential-field signatures of buried Precambrian basement in the Western Canada Sedimentary Basin

An internally consistent, levelled compilation of magnetic data is derived for Alberta and northeastern British Columbia. With Bouguer gravity data, t his compilation is used to refine the definition of Precambrian basement do mains within the Western Canada Sedimentary Basin. Magnetic data are draped at a constant distance above the mapped basement surface to reduce the eff ects of varying magnetic source depths. Automated interpretation methods th at effectively map outlines of magnetic sources are used to characterize th e internal structure of the domains and to aid in their delineation. The ba sement domain map thus derived differs from previous interpretations in the extension of domains further to the southwest, due mainly to the availabil ity of new public-domain magnetic data and the more precise definition of d omain boundaries, based on the magnetic source location maps. The Nahanni, Hottah, Chinchaga, Thorsby, Vulcan, and Kiskatinaw domains are weakly magne tic and characterized by magnetic sources that are paramagnetic, comprising low-susceptibility silicate minerals. All other domains are characterized by the presence of ferrimagnetic material, most likely magnetite, which has a sufficiently high susceptibility to produce measurable anomalies. The la rgest anomalies and magnetizations are found in the Fort Nelson, Fort Simps on, Buffalo Head, Talston, Ksituan, and Matzhiwin domains. Such large magne tizations are usually indicative of intermediate igneous rocks associated w ith magmatic arc environments. Moderate-amplitude anomalies and (or) magnet izations are characteristic of the Nova, Wabamun, Lacombe, Rimbey, Loverna, and Medicine Hat domains, suggesting the presence of ferrimagnetic basic a nd granitoid rocks. Within some of the moderately magnetic domains are area s of paramagnetic lithologies that produce no magnetic anomalies. The narro wer regions of magnetic lows, such as the Thorsby, Kiskatinaw, and Vulcan d omains, are interpreted as resulting from demagnetization effects accompany ing collision. Since demagnetization zones are limited in areal extent, the wider, more extensive magnetic lows of the Chinchaga and Hottah domains li kely result from a combination of boundary demagnetization and a lower bulk magnetization level of crustal lithologies present.