A magnetotelluric study of the southwestern Northwest Territories,
Canada

X. Wu, I.J. Ferguson, Department of Geological Sciences, U. of
Manitoba, Winnipeg, MB, Canada, R3T 2N2, E-mail: umwux@cc.umanitoba.ca
A.G. Jones, Geological Survey of Canada, 1 Observatory Crescent, Ottawa,
ON, K1A OY3, Canada

    As part of the LITHOPROBE SNORCLE (Slave-Northern Cordillera 
Lithospheric Evolution) Transect, magnetotelluric soundings were 
made at 58 sites in southwestern Northwest Territories, Canada. The 
sites cross the exposed Archean Slave Province and the buried Proterozoic 
Hottah, Fort Simpson, and Nahanni terranes. The objectives of the 
present study are to resolve the conductivity structure of the crust and 
mantle lithosphere of the Proterozoic terranes and overlying Phanerozoic 
sediments.  Acquisition at each site included both wide-band, using 
Phoenix V5 systems, and long periods, using GSC LiMS instruments. At the 
geomagnetic latitudes of survey the responses are potentially contaminated 
by non-uniform sources requiring application of robust processing methods.
Groom-Bailey decompositions and static-shift removal were applied in 
data analysis.
       The MT responses indicate that at shallow depth the conductivity 
structure is approximately 1D. Within the bulk of the crust it is 2D with 
a strike ~N30E. At greater depth it is 2D with again a strike ~N30E except 
on the Great Bear magnetic arc where it is weakly 2D with a direction ~N30W. 
Apparent resistivity and phase sections reveal both lateral and vertical 
conductivity variations.  A conductive surface layer, corresponding to Phanerozoic 
cover, thickens from east (0 m) to west (1000 m), with the most conductive 
rocks occurring at several hundred metres depth.  A relatively resistive 
crust overlies a more conductive region at depth. Longer-period (>1 s) spatial 
variations in several groups of sites correspond with tectonic boundaries. 


Session 9:  Local and regional electromagnetic studies.