NEOTECTONIC FEATURES IN SOUTHERN ONTARIO: AN IN-DEPTH ANALYSIS OF POP-UP STRUCTURES AND IMPLICATIONS FOR SEISMIC RISK

Abstract

Intraplate tectonics is generally not well documented and understood, despite its significance for seismic hazards in areas such as southeastern Canada. Neotectonics is even less well understood in these regions. This study focuses on providing an in-depth analysis of potential neotectonic pop-up structures in southern Ontario, Canada, leading to a comprehensive definition of what pop-up structures are, to constrain the processes involved in neotectonism, and to determine the extent to which neotectonism impacts the region. Previous literature has hypothesized that neotectonic structures have a likely potential to be linked to reactivated structures within the Precambrian Basement rocks of the Canadian Shield. In addition to documenting new potential neotectonic structures, this work provides a brief overview of tectonics in southern Ontario, and how previously measured lineaments in the Precambrian Basement may align with observable, potentially neotectonic surface structures. Three locations in southern Ontario were documented using a combination of ground and drone-based structural analysis: 1) Fletcher Creek Ecological Preserve, 2) Wainfleet Wetlands Conservation Area, and 3) multiple sites on Manitoulin Island. These sites were chosen where previous studies had documented neotectonic activity, and/or where initial geomorphic analyses indicated the possibility of a pop-up structure. All sites are located within the Silurian to Devonian cover rocks of the Niagara Escarpment. Fracture patterns at each site were analyzed using ground-based measurements using FieldClino and/or drone-based photogrammetry (DJI Phantom 4 V2 and Phantom 4 Pro acquisition followed by analysis in Pix4D and Drone2Map), where applicable. Where access permitted, ground-based measurements iv were obtained on structures, in addition to RTK-DGPS (Real Time Kinematic Differential Global Positioning System) profiles over potential pop-up structures. Analysis revealed that pop-up structures exhibit a distinct geomorphic expression, manifesting as a near-linear elevated ridge, where stress relief features have variable geomorphic expressions, such as domes. In southern Ontario, the presence of these pop-ups and stress relief features demonstrates that the region is tectonically active, despite often being characterized as a stable continental interior. This study adds to a growing body of work documenting neotectonics in southern Ontario, with several stress-related structures documented for the first time in this study, showing their prevalence over a wide area. The results of this study were used to create an updated tectonic hazard map of Ontario.