The North Range contact of the Sudbury intrusive complex: An integrated interpretation

High resolution seismic reflection data from the LITHOPROBE Abitibi-Grenville transect across the Sudbury Structure has suggested a simple intrusive contact for the boundary between the Levack Gneiss and the North Range Norite of the Sudbury Igneous Complex (SIC) (Milkereit et al, 1992). The same profile also suggests that the constituent members of the SIC along the North Range form a simple layered sequence. Models derived from regional gravity and aeromagnetic coverage tend to support this interpretation. High resolution helicopter aeromagnetic data reveals that locally, the contact is more complex. Radiometric studies along this contact have provided evidence of fluid alteration post dating the intrusion of the main mass of the SIC (Deutsch et al., 1989) supporting a more complex contact interpretation. A paleomagnetic survey completed along a surface profile extending from Webfoot Lake in the Levack Gneiss across the contact with the North Range of the SIC in the vicinity of the Strathcona Mine defines a zone of remagnetisation that is coincident with the distribution of thermally reset plagioclase recrystallization. Superficially the North Range contact appears to be a simple intrusive contact. Paleomagnetic examination of SIC samples from a continuation of the traverse between the Strathcona and Fraser Mines in addition to samples obtained from underground workings at the Strathcona Mine reveal two divergent remanence directions, suggesting that the contact has been modified by at least two post-SIC remagnetisation events. Paleomagnetic and rock magnetic property studies also define a zonation within the felsic norite thought to have developed as a result of deuteric alteration.