Electrical Resistivity Structure of the Proterozoic Grenville Province Lithosphere
Electrical Resistivity Structure of the Proterozoic Grenville Province Lithosphere
Previously Published Material: This work forms part of a PhD thesis and a manuscript based on this presentation is still under review with Geophysical Journal International.
Abstract ID#: 35165
English Abstract:
The large-scale lithospheric resistivity images structure of the Proterozoic Grenville Province and its margin with the Archean Superior Province in southern Ontario is investigated with 84 MT sites, distributed across southern Ontario. Dimensionality analysis indicates dominantly 2-D resistivity structure below the Grenville Front and northwestern Grenville Province, with more significant 3-D responses to the southeast. It allows the division of the lithosphere into upper (45-150 km) and deeper (>200 km) mantle layers with regional strike azimuths of N85oE (±5o) and N65oE (±5o) respectively. The entire Grenville Province in southern Ontario is characterized by large-scale, laterally extensive, resistive lithosphere. The top of this feature is at about 45 km depth and the geometry of its base shows that the true thickness of the lithosphere in this region is about 280 km. This resistivity anomaly extends for about 300 km southeast of the GF from the exposed Superior Province and along strike for at least 800 km. This feature is interpreted to be Superior Province lithosphere and the corresponding N85oE geoelectric strike to be associated with the fabric of the Superior Province. This Archean lithospheric root provided the stable basement for the Grenville orogen. A large region of enhanced conductivity in the lower lithosphere is attributed to the refertilization of the mantle lithosphere by fluids associated with the Cretaceous kimberlite magmatism. The results provide evidence for refertilization of a large volume of the lower mantle lithosphere by the passage of fluids. The enhanced conductivity is interpreted to be associated with the presence of water in nominally anhydrous minerals. A water content of 50 wt ppm was estimated based on average crustal heat flow, average resistivity at 180 km depth and temperature of 1220oC. It is hypothesized that the strike direction measured in the deeper mantle of the study area was established in the Cretaceous and potentially records the plate motion at that time.