Geophysical and structural evidence for the presence of a central uplift in the South Range of the Sudbury impact structure

The Sudbury Structure formed as a large impact crater. The current roughly elliptical outcrop pattern shows that the originally near circular crater has been subject to post-impact deformation. Some features of the original crater morphology have been preserved. For example, the arcuate form of the North Range is explained by preservation of the crater wall. This study examines data from the South Range of the Sudbury Structure. Dip and dip direction measurements on the basal contact of the Sudbury Igneous Complex (SIC) and cumulate layering within the norite are examined for lateral continuity across the South Range. Sites within a “wedge” bounded by the Whitewater Lake Fault Zone and the Whitson Lake Shear Zone have dips that are systematically different to sites located in the area to the west. Paleomagnetic results from sites in the norite and Offset dikes of the South Range record three periods of remanence acquisition. Comparison of paleomagnetic results between different Ranges of the SIC indicate the three remanence components record the initial emplacement of the melt sheet and two later metamorphic events. The lack of any systematic dispersion within each remanence component across the South Range means that the differential dips between the “wedge” and the adjacent area must have formed before acquisition of the earliest remanence acquisition. A viable explanation is that the differential dip is associated with preservation of a remnant of the central uplift/peak ring of the original impact crater. The internal coherence of directions within each remanence group requires the South Range, even though showing evidence of localized internal deformation, was rotated into its current position as a solid body.