The interpretation of magnetotelluric measurements from the Glennie Domain to the Flin Flon Belt, eastern Saskatchewan, part of the lithoprobe, trans-hudson orogen transect

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Stevens, Kevin Maxwell
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During 1992 broadband magnetotelluric (MT) and audiofrequency magnetotelluric (AMT) surveys were completed on a continuous profile across the Trans-Hudson Orogen. These surveys followed the LITHOPROBE deep seismic reflection survey along the transect. Data from twenty-eight AMT and MT sites along the LITHOPROBE transect have been analyzed in order to resolve the electrical conductivity structure of the crust and subcrustal lithosphere in the GD-HLB region. Detailed analysis of the MT data using dimensionality and directionality methods including induction vectors and Groom-Bailey tensor decomposition, identified frequency ranges in which groups of MT sites have a quasi-two dimensional MT response and a geologically plausible strike. Analysis of the data from 14 AMT/MT sites located on the Phanerozoic cover overlying the Glennie Domain showed that a one dimensional (1-D) interpretation provides a reasonable representation of the resistivity structure of the Phanerozoic sedimentary cover and upper crustal structure. Apparent resistivity and phase pseudo-sections show similar responses for both MT polarization modes. One dimensional and two dimensional (2-D) inversion of data from the sites on Phanerozoic cover was done using both the Bostick transform and the Occam inversion methods. Examination of the other two MT data sets showed that these data could be treated using a 2-D approach. This analysis indicated a large scale, layered conductivity structure, dipping east, a model which is in good agreement with the geological interpretation provided by the seismic data. These data also provided direct evidence that the TFZ and SWT are both low resistivity features ($<$1000 $\Omega$.m). Additional 2-D analysis was performed to assess the MT results. (Abstract shortened by UMI.)