Tectono-Geomorphic Mapping of Neotectonic Bedrock Structures Using Topobathymetric Modelling and Near-Surface Geophysics (Prince Edward County, Ontario, Canada)

Abstract

The causes of recurrent, low to moderate magnitude (≤ 4 Nuttli Magnitude – MN) intraplate seismicity in Southern Ontario are not well understood. Neotectonic faults and pop-up structures have been identified in Prince Edward County (PEC), but their links to underlying basement-fault zones and regional seismicity is uncertain. Tectono-geomorphic mapping and near-surface geophysics were conducted in this study on the Long Point peninsula (PEC) to investigate possible neotectonic structures. A high-resolution (2 m) digital topobathymetric model (TBM) was constructed by combining a LiDAR (Light Detection and Ranging) derived terrain model with multi-beam sonar bathymetric data. Six bedrock fault zones and > 30 pop-up structures were identified in the TBM, including a distinct, low relief (< 2 m) bedrock ridge (Gravelly Bay Fault Zone - GBFZ) that crosscuts late Pleistocene (ca. 12 ka) drumlin features. Ground-penetrating radar profiles reveal localized thrust faulting, block rotations and increased fracture density within the fault damage zone. The GBFZ is aligned with a NNW-trending magnetic lineament in Lake Ontario, indicating a coincident fault or shear zone in underlying Precambrian basement. Fault mechanisms for the GBFZ could include glaciotectectonic thrusting of bedrock, post-glacial isostatic unloading and reactivation of favourably oriented faults under the current intraplate stress field. The spatial coincidence of the GBFZ with basement magnetic lineaments suggests that the fault zone is structurally inherited from a fault or shear zone in the underlying Mesoproterozoic basement. The Picton and Salmon Point faults are also located over NE-trending aeromagnetic lineaments, indicating ‘tectonic templating’ of Paleozoic faults by underlying Precambrian basement structures. Further geophysical and field structural studies are underway in PEC to determine the fault mechanisms and possible linkages to recurrent seismicity in Southern Ontario.