An evaluation of the conductivity structure of the Northwest Superior Province, Canadian Shield, using the magnetotelluric and audiomagnetotelluric methods

As part of LITHOPROBE's goal for the West Superior Transect of determining how the Archean continental lithosphere formed by accretionary processes, 51 magnetotelluric (MT) sites have been acquired in the northwestern portion of the Superior Province of the Canadian Shield. Sites extend from the Phanerozoic cover of the Hudson Bay Lowlands to the English River subprovince. A total of 41 MT sites and ten audiomagnetotellurics (AMT) sites were used to evaluate the crustal structure of the Northwest Superior Province and Fox River Sill respectively. This examination of the dataset will discuss the collection of the data, describe the data analysis, and present inversion results along with geological interpretations.; MT results indicate the northwest Superior Province has a complex two-dimensional electrical conductivity structure with corresponding geoelectric strikes oriented at an azimuth of 120°. Mapped faults, dykes and lineaments coincide with geoelectric strike determinations. Transitions in electrical conductivity coincide with subprovince boundaries defined by the surface geology. Observed apparent resistivities are high throughout the northern Superior Province.; Two-dimensional inversions of the MT data have been done to obtain models of the subsurface resistivity structure of the Northwest Superior Province and the Trans-Hudson Orogen basement beneath the Hudson Bay Lowlands. A range of data subsets and inversion parameters were used in order to examine the resolution of the models. The results show that the surface sedimentary rocks of the Hudson Bay Lowlands are defined by a conductive wedge. The overall resistivity of the crust in the northwest Superior Province is greater than that seen in the southwest Superior Province. There are also resistivity structures observed in the middle to lower crust. Observed variations in mantle resistivity can be interpreted in terms of models for the tectonic evolution of the region and suggest subduction occurred beneath the northern margin of the Superior province as well as beneath the southern margin of the North Caribou terrane.; The Fox River Sill exhibits a complex conductivity structure with transitions in resistivity coinciding with mapped geological units. The geoelectric strike of near-surface rocks is east-west but a conductor in the Lower Central Layered Zone exhibits a strike of 120°. The conductive body appears to dip to the southwest towards the Marginal Zone.; The resistivity structure of the subsurface across the northwest Superior Province has been resolved at reconnaissance scale and a detailed resistivity profile across the Fox River Sill has been constructed. This study will serve as the launching point for future work, for example incorporating static effects and 3-D modelling.