Abstract
An integrated approach using both geomagnetic depth-sounding (GDS) and magneto-tellurics (MT) is applied to the determination of the electrical conductivity structure in western Canada; 42 GDS stations and 6 broad-band MT stations are used. These data are combined with other geophysical information to provide self-consistent petrological models. Excluding geochemically improbable solutions, it can be shown that: a) temperatures at depth 35km must be at least 750°C in the entire western region (eastwards extent undefined); b) in a smaller, sharply defined, region (eastern boundary within about ±50km of the Rocky Mountain Trench) the lower crust and possibly uppermost 10-25km of the mantle are hydrated, probably with partial melting.
