Regional 3D geophysical investigation of the Sudbury Structure

Abstract

The 3D geologic and structural setting of the Sudbury Structure was predicted by an integration of surface and subsurface geologic data with 2.5D modeling of high-resolution airborne magnetic and gravity data using 3D GeoModeller software. Unlike other CAD-based 3D software, GeoModeller uses the field interpolator method, whereby contacts of rock units are assumed to be equipotential surfaces, whereas orientation data determine the gradient and direction of the surfaces. Contacts and orientation variables are cokriged to generate 3D continuous surfaces for each geologic unit. Our 3D geologic model was qualitatively evaluated by forward computing the predicted gravity response at 1 m above topography and by comparing this response to the measured gravity field. Large-scale structures within the Onaping Formation and Archean basement, which overlie and underlie the Sudbury Igneous Complex (SIC), respectively, were not the cause of the linear gravity high in the center of the Sudbury Structure. We suggested that the deformation of the initial circular SIC may have commenced under the Sudbury Basin due to the reversal of the normal faults related to the Huronian rift system during the Penokean orogeny, therefore resulting into a north verging fold at the base of the SIC in the south range. This new interpretation was consistent with the magnetic and gravity data and honoured most of the significant seismic reflectors in the Lithoprobe seismic sections.