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.

Perceiving the Crust in 3‐D: A Model Integrating Geological, Geochemical, and Geophysical Data

“… Geophysical inputs used for the construction of the 3‐D model. The six cross sections derived from Olaniyan et al () (AA', BB', CC', DD', EE', FF') and the five cross sections extracted from the H14 model (MM', M'N', NN', MN, OO') are projected on the simplified geological map. The inner box represents the CUC.…”

“…For the remaining area of the CUC, the 3‐D geometries of the units were developed in H14 on the basis of surface contacts between units and 16 interpreted crustal cross sections of the area, with the main inputs from Easton () and Adam et al (). In this perspective, five virtual cross sections (MM', NN', MN, M'N', and OO' in Figure ) are extracted from H14 and used as input for inferring the structure of units not constrained by inputs from Olaniyan et al ().…”

“…Richard Ash for help with the ICPMS analyses. The authors are grateful to Oladele Olaniyan and Richard Smith for providing help and sharing data of the 3‐D model published in Olaniyan et al (). The authors appreciate the essential support and valuable insights from Mike Easton, Mark Chen, Nigel Smith, Eligio Lisi and Pedro Jugo.…”

“…The crustal structures of the nine units were defined by combination of multiple geological and geophysical inputs: (i) the contacts of the simplified geological map (Figure 4), (ii) a published digital elevation model [Jarvis et al, 2008], (iii) the map of depth of the top of the middle crust reported in H14, (iv) the 2.5D geological models along six profiles used for constructing the 3D model reported in [Olaniyan et al, 2015] and (v) five virtual cross sections derived from the model developed in H14.…”

“…Consequently, predictions of the abundance and distribution of the heat producing elements in this unit came with considerable uncertainties, resulting in a large variability on estimates of the local radiogenic heat power and expected geoneutrino signal at the SNO+ detector located in Sudbury. Based on these findings, we performed additional geochemical sampling (112 new analyses) of the region and combined these data with the models published in H14 and in [Olaniyan et al, 2015], to build a revised 3-D high-resolution model that describes the Close Upper Crust (CUC) corresponding to the 50 km × 50 km area around SNO+.…”