Electromagnetic signature of an ancient collision zone: the 
Trans-Hudson Orogen and the NACP


Juanjo Ledo,   University of Barcelona, Spain, and Geological Survey of Canada
               Ottawa, Canada
Alan G. Jones, Geological Survey of Canada, Ottawa, Canada 


The Paleoproterozoic Trans­Hudson Orogen (THO) extends from South
Dakota north through North Dakota and Saskatchewan, across Hudson Bay and is believed to extend into Greenland, with possible counterparts in Scandinavia.

Magnetotelluric studies along eight profiles from North Dakota to northern Saskatchewan map the NACP as a predominantly 2D structure. The NACP, as a 
multi­body structure, appears in all profiles, but it presents significant 
variation in its depth, horizontal position and extent, as well as its strike,
along its length. Due to the blanketing effect of the Paleozoic sediments, the 
multi­body structure cannot be distinguished from an anisotropic body. The 
Behaviour of both polarizations is very similar for the different profiles, 
except for the northernmost one due to the lack of the sedimentary Paleozoic 
layer at the surface. The profiles located in southern Saskatchewan and the 
northernmost one in North Dakota display bodies of enhanced conductivity deep 
in the crust, beneath the mid­crustal NACP. 

The tectonic implications of the location, geometrical shape and nature of 
the NACP will be the main topics of this paper


Session 9: Local and regional electromagnetic studies