The Sudbury structure: A circular impact crater?

Abstract

Petrological, geochemical, and structural evidence supports genesis of the Sudbury Structure by a meteorite impact. The Sudbury Igneous Complex (SIC) represents the ponded melt sheet. The primary morphology and size of the Sudbury Crater remains the subject of extensive discussion. A model is presented explaining the transformation of an originally circular crater to the current elliptical form. Processes involved in the geometrical transformation include; a) volume reduction through melt sheet crystallization, and repeated expulsion of melt into the surrounding footwall, b) translation and segmentation on multiple southeast dipping thrust surfaces, and c) relative displacement on steep north-northwest trending faults. Paleomagnetic, geochemical and structural evidence supports the concept of periodic melt expulsions into the footwall. Seismic, potential field and paleomagnetic surveys provide evidence in support of multiple thrust surfaces. After over 9 km of subsequent erosion only a small volumetric portion of the original SIC remains, although complete vertical sections through the melt sheet have been preserved. None of the crater wall has been preserved. Thus the contacts between the SIC and the footwall on the North and South Ranges are interpreted as uplifted crater floor margins.