Deformation of the Sudbury Structure

Tectonic processes similar to those occurring today have been active for a long time in the Earth's history, as documented by numerous fault zones and mountain ranges. A good example of tectonic deformation is found in the Sudbury structure in Ontario, the site of world-class Nickel and Copper mines. The favoured interpretation for the structure is that it was formed by the impact of an extraterrestrial body, some 1850 million years ago. However, the present day structure, as represented for example by the horizontal gravity gradient map, is not circular, as one would expect for an impact crater, but rather elliptical.

Map of the horizontal gravity gradient
over the Sudbury Structure (101k)

Using geological data that indicate that the region underwent a considerable amount of compression, the Sudbury Structure was reconstructed to what could have been its original shape, which is near circular.

Map of the horizontal gravity gradient
over the Sudbury Structure as it may
have looked shortly after formation. (101k)

This finding supports its interpretation as an impact structure. Efforts to understand the origin of the major mineral occurrences at Sudbury consequently have a significant bearing on our understanding of the economic potential of other impact craters in Canada and elsewhere.

Suggestion for further reading:

Roest, Walter R. and Pilkington, Mark; 1994; Restoring post-impact deformation at Sudbury: A circular argument; Geophysical Research Letters, 21, 959-962.

Deutshc, A. and Grieve, R.A.F.; 1994; The Sudbury structure: Constraints on its genesis from Lithoprobe results; Geophysical Research Letters, 21, 963-966.