Geophysical and structural evidence for Penokean age deformation of the East Range of the Sudbury impact structure

Shock metamorphic features prove the Sudbury Structure formed as an impact crater. Paleomagnetic, seismic, and stratigraphic evidence confirm an original near circular crater has been deformed into its current elliptical shape. Recent studies have identified attributes of the original crater: the arcuate form of the North Range is explained by preservation of the crater wall; variations in the lateral continuity of the basal contact and cumulate layering of the Sudbury Igneous Complex on the South Range are interpreted as evidence for the preservation of a central uplift. Herein we explain how the geometry of the East Range of the Sudbury Igneous Complex, which currently dips steeply to the west, is compatible with an impact origin for the Sudbury Structure followed by Penokean age tectonic deformation. Evidence for this is provided by: topographic data to estimate the location of fault zones; bedding orientation data to demonstrate the presence of a fault-related pattern of dip geometry; paleomagnetic data to constrain the timing, magnitude and orientation of post-impact tectonic rotations; and anisotropic magnetic susceptibility data to outline the spatial distribution of magmatic and tectonic related magnetic fabrics. An interpretation which satisfies all the available data involves progressive solid body rotation of the East Range as the impact melt sheet gradually crystallized (cooled). This Penokean age deformation was associated with regional scale vertical displacement on the N-S trending Upper Wanapitei fault.