ON THE NACP CONDUCTIVITY ANOMALY GEOPHYSICAL SIGNATURE

Juanjo Ledo, Alan G. Jones and Xavier Garcia
Geological Survey of Canada. 1, Observatory Crescent. Ottawa K1N 8Y3, ON. Canada.
e-mail: ledo@cg.nrcan.gc.ca, jones@cg.nrcan.gc.ca and garcia@cg.nrcan.gc.ca

The Paleoproterozoic Trans-Hudson Orogen (THO) extends from southern South 
Dakota north through North Dakota and Saskatchewan, then swings eastwards 
through northern Manitoba into Hudson Bay. The first geophysical evidence for 
the extent of the orogen was the North American Central Plains (NACP) 
conductivity anomaly discovered by discovered by Gough and colleagues in the late 1960s and early 1970s using a GDS array survey.

In this paper, we present the results of the natural-source magnetotelluric 
(MT) studies along nine profiles from North Dakota to the exposed orogen in 
Saskatchewan. The NACP anomaly had been associated with metasedimentary 
sequences deposited between the advancing La Ronge arc and Rae-Hearne Archean 
hinterland. Analysis of hand sample rocks in the exposed orogen had shown that 
the only conductive rocks belong to a sedimentary unit that contains sulfides. 
The trace of the NACP anomaly is very uniform along all the profiles, except 
for profile N, where it reaches its maximum width.

Valid geodynamic models of the orogen must explain both, the enhancement of 
the conductivity and the trace of the anomaly. In addition, a comparison 
between the MT and seismic profiles is shown where are spatially coincident.