A geomagnetic induction anomaly in southeastern British Columbia has been investigated in detail with a 20-station network. The results indicate a sharp (near vertical) discontinuity in deep electrical conductivity structure, trending roughly east–west and located at the south end of Kootenay Lake. It is interpreted as evidence for sinistral strike–slip which intersected the edge of the main conductive layer which underlies most of the western Cordillera.Geological evidence indicates that such a feature (which has no known surface expression) must predate the late Paleozoic or early Mesozoic (200–250 m.y.). The persistence of sharp discontinuities over such long periods would confirm the compositional, rather than thermal, nature of the lower crustal conductive layer under the western Cordillera.

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