Electrical-resistivity imaging of the central Trans-Hudson orogen

Abstract

Magnetotelluric (MT) measurements were made on a profile across the Trans-Hudson orogen in 1992 as part of the Lithoprobe transect. The present study includes analysis of results from a 300 km-long section of the profile in which allocthonous Paleoproterozoic juvenile terranes and arc rocks of the western Trans-Hudson orogen have been juxtaposed against the Archean Sask craton. Impedance tensor decomposition of data from the 40 MT sites in the area indicates a geoelectric strike of N28°E. Two-dimensional inversion of the data using a non-linear conjugate gradient algorithm provided images of the resistivity structure. Resistivity images reveal that the crust of the Sask craton is relatively resistive (>2000 Ω·m). In contrast, the rocks of the Flin Flon belt, Glennie domain, and La Ronge domain are mostly relatively conductive (<100–1000 Ω·m). In the east of the study area, the images suggest that the Tabbernor fault juxtaposes more conductive rocks of the Glennie domain in the west against more resistive Archean rocks in the east in the upper 20 km of the crust. In the west of the study area, the images confirm that the North American Central Plains conductor occurs within westward-dipping rocks of the La Ronge domain. The resistivity images also reveal that the lower crust beneath the west of the Glennie domain, within a crustal culmination defined by seismic reflection data, is electrically conductive (<100 Ω·m). An explanation for the enhanced conductivity is that part of the lower crust beneath the western Glennie domain is of Proterozoic age. In this case, a possible source for the enhanced conductivity, based on its location at the edge of the Sask continental block, is Proterozoic ocean margin rocks.