A trishear model for the deformation of the Sudbury Igneous Complex, Canada

摘要

The Sudbury Igneous Complex (SIC), Canada, is an impact-induced layered sheet of crystalline rocks deformed into an asymmetrical fold basin, the Sudbury Basin. The basin geometry at depth is largely unknown as few attempts were made to quantify displacement and rotation of layer contacts. We propose that the dip of layer contacts, and foliation surfaces in the southern SIC can be approximated by trishear fault propagation folding. Trishear deformation accounts for: (1) angular discordances between upper and basal SIC contacts, (2) local overturning of the SIC, (3) progressive steepening of foliation surfaces from NW to SE, (4) strain gradient in the Sudbury Basin sedimentary rocks, and (5) thickness variations in SIC layers. Moreover, the South Range Shear Zone, a zone of moderately strong metamorphic fabrics, coincides with the surface manifestation of the proposed trishear zone.