Hydrochronology of a proposed deep geological repository for low- and intermediate-level nuclear waste in southern Ontario from U-Pb dating of secondary minerals; response to Silurian and Cretaceous events

• Published in: Canadian journal of earth sciences Vol. 57; no. 4; pp. 464 - 476
• Main Authors: Davis, D. W, Sutcliffe, C. N, Thibodeau, A. M, Spalding, J, Schneider, D, Cruden, A, Adams, J, Parmenter, A, Jensen, M, Zajacz, Z
• Format: Journal Article
• Language: English
• Published: Ottawa National Research Council of Canada 01.04.2020; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: absolute age; Analysis; Bruce County Ontario; Bruce Nuclear Generating Station; Calcite; Calcite crystals; Canada; carbonate platforms; Carbonate rocks; Carbonates; Chemical analysis; Cretaceous; Dating; Devonian; Direction; Eastern Canada; Engineering geology; Exposure; Fluid dynamics; Fluid flow; Geochronology; Hot spots (geology); hydrostratigraphy; Hydrothermal fluids; Hydrothermal solutions; Infiltration; Lead; lithostratigraphy; Mesozoic; Minerals; Nuclear facilities; Ontario; Ordovician; Outcrops; Paleozoic; Perturbations; Plates; Plates (tectonics); Platforms (geology); radioactive waste; Radioactive wastes; Radiometric dating; Seawater; Sedimentary rocks; Sequencing; Silurian; site exploration; tectonics; U/Pb; veins; Veins (geology); Volcanic hotspots; waste disposal; waste disposal sites; Water analysis; Canada; Ontario; Quebec; New England; Ontario Canada
• ISSN: 0008-4077; 1480-3313
• DOI: 10.1139/cjes-2019-0004

A record of fluid flow has been documented within a Paleozoic carbonate platform sequence by U-Pb dating of calcite in veins and vugs from rock core sampled through a shallowly dipping sequence of sedimentary rocks beneath the Bruce nuclear site, Ontario, Canada. Secondary calcite from >650 m deep Ordovician carbonate rocks yields a Silurian age of 434 ± 5 Ma possibly related to infiltration of seawater from overlying evaporitic basins as well as hydrothermal solutions that infiltrated from below. In contrast, near-surface Devonian rocks mostly give vein infill ages over the range of 80-100 Ma with evidence for younger infill down to 50 Ma. Vein calcite samples previously dated from surface outcrops of Ordovician carbonate exposed up to 500 km to the east yielded similar U-Pb ages. Coincidence of near-surface vein calcite ages indicates widespread vein emplacement synchronous with a change in direction of motion of the North American plate as well as possible erosional unroofing following passage of the region over the Great Meteor hotspot approximately 125 Myr ago. Deeper carbonate formations have remained apparently impermeable to post-Paleozoic disturbance despite these perturbations.