Crustal and lithospheric scale structures of the Precambrian Superior-Grenville margin

The lithosphere beneath the margin of the Archean Superior and Proterozoic Grenville provinces was investigated with a northwest-southeast oriented, 650-km-long profile of 40 magnetotelluric stations. Dominant geoelectric strike azimuths of N45°E and N85°E were defined for the crust and the lithospheric mantle respectively. A 2-D isotropic resistivity model derived using the crustal strike images resistive Laurentian margin rocks dipping southeast to the base of the crust, bounded to the northwest by the Grenville Front, and to the southeast by the Central Metasedimentary Belt Boundary Zone. The observation is in contrast to conductive mid to lower crust elsewhere in the region. A 2-D isotropic resistivity model determined using the lithospheric mantle strike azimuth reveals an extremely resistive region in the upper 100. km of the mantle lithosphere of the northern Grenville Province. The geometry of this body, which includes a well-defined base and southeast dip, suggests that it is Superior lithosphere. A sub-vertical conductor, located approximately 50. km along strike from the Mesozoic Kirkland Lake and Cobalt kimberlite fields, is interpreted to be due to re-fertilization of an older mantle scar. The resistivity model includes a horizontal conductor at 160. km depth beneath the southern Superior Province that is possibly the resistivity signature of the lithospheric-asthenospheric boundary.