High‐frequency magnetotelluric investigation of crustal structure in north‐central Abitibi, Quebec, Canada

Abstract

Thirty‐one audiomagnetotelluric (AMT) soundings have been collected along a N‐S profile across the northern Abitibi greenstone belt. The recording frequency ranges of 10000‐1 Hz for 25 stations and 10000‐0.001 Hz for the other six stations were appropriate for defining the near‐surface geoelectric structures and for imaging major faults and shear zones down to approximately 10 km along the profile. Six time‐domain electromagnetic (TEM) soundings were also collected near the southern end of the profile, to provide a correction for static shift. Extensive static distortion analysis reveals that most of the AMT data are not distorted by localized near‐surface structures; however, they are affected by static shift. In order to remove this static shift, a spatial filter was designed and applied to the data, effectively reducing static shift as verified by TEM soundings at the same sites. Extensive 2‐D inversions of the filtered data were carried out. The results suggest the presence of a thin overburden with both conductive and resistive blocks overlying a very resistive basement. Among the four geological deformation zones crossed by the profile, only two zones are imaged as subvertical conductive crustal structures extending to the limit of resolution of AMT. These correspond to, major breaks (Porcupine‐Destor Fault and Casa Berardi Tectonic Zone) as evidenced by the seismic reflection data collected over the same area. Copyright © 1995, Wiley Blackwell. All rights reserved