The importance of lithological heterogeneity of the Onaping Formation for understanding post-impact deformation of the Sudbury Impact Structure, Canada

Abstract

The suevitic Onaping Formation overlies the layered Main Mass of the 1.85Ga Sudbury Igneous Complex (SIC) of the Sudbury Impact Structure, Ontario. The Formation consists of four Members, namely from top to bottom, the Black, the Green, the Gray and the Basal. Post-impact NWSE shortening during the Penokean Orogeny (ca. 1.9–1.75 Ga) affected the Onaping Formation and led to the lobate shape of the SIC in plan view. In order to investigate the possible fold origin of the NE-lobe of the SIC, a field-based structural analysis of the Onaping Formation was conducted in the Frenchman Lake area. The analysis is based on structural measurements at 580 stations and encompasses the orientation of mineral shape fabrics as well as their intensity. In addition to these quantities, lithological variation and metamorphic overprint of the Onaping Formation was examined. Special attention was paid thereby to the Green Member since previous workers stated that it forms a continuous unit at the base of the Black Member...