INDUCTIVE SOURCE EM SOUNDING OF THE SUDBURY STRUCTURE

A controlled source electromagnetic survey conducted in the South Range of the Sudbury Igneous Complex has revealed a south dipping conductive zone at depths of three to five kilometers. The zone has a conductance of about seven siemens whereas the overlying rocks total less than one siemens, indicating the feature is well resolved by the data. The anomalous conductivity may be derived from graphitization of the carbonaceous Black member of the Onaping Formation. Presence of a graphitic conductor is compatible with a model of tight folding or thrusting of the southern portion of the original Sudbury structure over the northern part along a basal plane defined in the Onaping Formation. Graphite could provide the mechanical lubrication to decouple the North Range from the tectonic deformation of the South Range.