Morphology and tectonic modification of the Sudbury impact crater: the North Range

Abstract

The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20°, and differing magnetic fabrics in the norite/gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC are established using dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show (a) the elliptical form of the North Range is a primary feature associated with a near-circular impact crater, (b) some of the original crater wall must have been preserved, and (c) deformation of the North Range is limited to regional scale block rotation producing a southwest dip modified by minor block rotation tilting and vertical displacement associated with north–northwest-trending faults.