3-D kinematic restoration of the eastern Sudbury Igneous Complex, Canada, and its importance for Cu-Ni-PGE sulphide exploration

Abstract

Kinematic restorations of deformed igneous terranes have rarely been attempted due to the general absence of (1) planar primary lithological contacts, (2) tightly constrained deformation kinematics, and (3) geometric constraints on lithologies and structures at depth. Because of the vast number of exploration drill holes, the deformed and layered 1.85 Ga Sudbury Igneous Complex (SIC) in Ontario, Canada, is reasonably well understood with respect to (1) and (3). We therefore explored the kinematics of folding and faulting in the eastern SIC and use the subsurface geometry of faults extracted from a model integrating surface mapping and drill core logs in an attempt to restore the geometry of part of the SIC. Specifically, we identified rotation magnitudes and the tilt axis of a kilometer-scale plunging fold, the West Bay Anticline, which appears to have folded the eastern part of the SIC. We combined a 3-D model of the faults and lithological contacts of the SIC, fault kinematics calculated from the inversion of brittle shear faults at surface, and limb rotations of the West Bay Anticline to kinematically restore the eastern part of the SIC. Results of restorations using simple shear and flexural-slip algorithms highlight the importance of slip on prominent, curved faults that displaced the SIC and facilitated its folding. Flexural slip appears to be the more plausible mechanism of the two, as it removed the curvature of, and displacement on, prominent faults. Flexural-slip restoration helps to estimate primary thickness variations of the SIC and the results show that thickened parts of the Main Mass of the SIC correspond spatially with known Cu-Ni-PGE sulfide deposits. This result demonstrates that 3-D restoration can be an important tool for mineral exploration in igneous terranes.