Seismic imaging of the enigmatic Sudbury Structure

Abstract

The Sudbury Structure on the southern margin of the Superior craton was created by a catastrophic explosion in 1.85 Ga and hosts one of the world's largest Ni‐Cu reserves. As a unique terrestrial geological feature, its genesis has been vigorously debated for more than a century. In an effort to optimize the image from seismic reflection data acquired across the center of the Sudbury Structure, we have developed a straight‐line common midpoint binning strategy and employed cross‐dip corrections. These pseudo‐three‐dimensional seismic processing techniques, coupled with standard processing methods, have overcome limitations associated with conventional two‐dimensional seismic data processing and have substantially enhanced the seismic image, warranting a more detailed and reliable structural interpretation. The new image has revealed a major, previously unrecognized, zone of imbricated NW thrusts. Interpretation of these thrusts provides critical timing constraints relating the Sudbury tectonic deformation to deposition of the Sudbury Basin sediments. The Onwatin argillites are penetrated by blind thrust faults, whereas the overlying Chelmsford turbidites are undeformed and most likely postdate the thrusting. Thus the uniform paleocurrent trends observed in the Chelmsford reflect subsequent deformation history and may be dismissed as evidence against an impact origin. Based on our interpretation of the seismic image, the original volume of the Sudbury Igneous Complex, likely an impact melt sheet, is ∼1 × 104 km3, supporting the claim that the Sudbury Structure represents the eroded and tectonized remanent of one of the largest known impact structure (∼200 km) on Earth.