Electromagnetic Crustal structure of southern and central Canadian Cordillera

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

The western margin of the Canadian Cordillera has grown by lithospheric 
accretionary processes since the Jurassic. The crust of the Canadian 
Cordillera is formed by terranes originated due to the consumption of 
oceanic plates beneath Ancestral North America craton and docking of their
exotic terranes on top of the craton.

To first approximation, the upper crust of the Canadian Cordillera is 
characterized by high electrical resistivity compared with the more conductive 
lower crust. However, a more intense study of the data reveal that the 
electrical structures are also characterized by important lateral changes at 
all scales, being the electromagnetic response for short periods variable 
from nearby sites. Previous studies had shown a strike variation with depth, 
being around N15E degrees in the lower crust, and in the upper crust being 
more erratic. The regional electric structure can be considered as a 3D upper 
crust over a 2D lower crust. Moreover, in some areas the relationship between 
the apparent resistivities and the phases doesn't follow a Hilbert transform 
relationship, which suggest important 3D effects.

The main topic of this paper is to present a regional electrical structure of 
the Canadian Cordillera crust to explain the main features of the MT data and 
its interpretation in terms of the known geological features of the region.


Session 9: Local and regional electromagnetic studies