Magnetotelluric data recorded in the period range 102--2.104 s using 100 km telluric dipoles in western Quebec, Canada, yield impedance estimates free from galvanic distortion and static shift. Analysis of the apparent resistivity, phase and magnetic transfer function data favors a regional 1D anisotropic model for the subsurface resistivity structure in the Abitibi Subprovince; lower resistivity direction of the anisotropy is EW, parallel to the main fault system. Joint 1D inversion of both principal impedances indicates a conductivity anisotropy in the upper and middle crust and in the upper mantle. It might originate for all depths from the same tectonic mechanism, mainly a NS shortening followed by an EW dextral shearing in the Archean. ¿ 1998 American Geophysical Union