Imaging the mantle lithosphere of the Precambrian Grenville Province: large-scale electrical resistivity structures

The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province in southern Ontario, Canada is investigated using 84 magnetotelluric (MT) sites divided into four profiles. Depth-based regional geoelectric dimensionality analyses of the MT responses indicate that the mantle lithosphere north of Lake Ontario can be subdivided into upper (45– 150 km) and deeper (>200 km) lithospheric mantle layers with regional strike azimuths of N85◦E (±5◦) and N65◦E (±5◦), respectively. MT responses from the Grenville Front and the northwest part of the Central Gneiss Belt are compatible with the presence of 2-D resistivity structures but farther to the southeast, in the southeast part of the Central Gneiss Belt and Central Metasedimentary Belt, they suggest the presence of localized 3-D structures. 2-D inversion of distortion-free MT responses images a large scale very resistive (>20 000 m) region that extends 300 km southeast of the Grenville Front and for at least 800 km along-strike in the lithospheric mantle beneath the Grenville Province. This feature is interpreted to be Superior Province lithosphere and the corresponding N85◦E geoelectric strike to be associated with the fabric of the Superior Province. The base of the resistor reaches depths of 280 km on two of the three MT profiles north of Lake Ontario and this depth is interprete