ELECTRICAL-RESISTIVITY STRUCTURE OF THE FLATHEAD BASIN IN SOUTHEASTERN BRITISH-COLUMBIA, CANADA

In June 1985, wide-band magnetotelluric data were acquired at 12 equally spaced sites along a 30 km profile crossing the Flatheat (Kishenehn) Basin in southeastern British Columbia, Canada. These data have been modelled by both one-dimensional inverse techniques and two-dimensional forward trial-and-error fitting. The results indicate the presence in the area of the following three major zones of low electrical resistivity (10-500 Ω.m): 1) Sediments of the 10 km wide Flathead sedimentary basin, extending to a depth of about 2 km, dominate the responses in the middle of the profile. 2) In the eastern part of the profile a thin (≃1 km) zone of low resistivity (35 Ω.m) is imaged at a depth of some 3 km extending eastward from the edge of the basin. We associate this zone with the less dense thrusted Mesozoic clastic rocks lying directly below the Proterozoic rocks of the Lewis thrust sheet. 3) Beneath the Flathead Basin is a third zone, of higher resistivity (500 Ω.m), which extends to deep within the crust. This zone may originate from mantle upflow. -from Authors