Exhumation history and tectonic inheritance of the Frontenac Arch (SE Ontario, Canada) from low-temperature thermochronology

The Frontenac Arch is a low-relief, NW-SE–oriented exposure of Grenvillian basement that connects the southeastern Canadian Shield with the Adirondack Mountains in the United States. The absence of low-temperature thermochronological constraints has limited our understanding of how this feature participated in, or responded to, Phanerozoic tectonic and erosional processes within a structural corridor oriented perpendicular to the dominant Grenvillian fabric. Here, we present new multisystem low-temperature thermochronological data from 19 crystalline Grenville samples collected along three transects across the Frontenac Arch, including apatite fission-track (AFT) analyses and apatite and zircon (U-Th)/He (AHe and ZHe) analyses. These data were integrated with inverse time-temperature modeling using QTQt to reconstruct the late-stage upper-crustal thermal history of the Frontenac Arch in the context of burial and erosion and to assess its regional tectonic implications. Single-grain dates exhibit substantial intrasample dispersion ranging 243–19 Ma for AHe, 732–114 Ma for ZHe, and AFT central ages of 208–109 Ma, reflecting partial to complete resetting of low-temperature thermochronometers. Thermal models indicate that the Paleozoic was characterized by reheating to peak temperatures of ~115–140 °C across much of the arch, and locally up to ~180–190 °C during the Carboniferous. Assuming a geothermal gradient of 25–35 °C/km, these temperatures are interpreted to record burial beneath ~2.7–5 km of Paleozoic sedimentary cover, locally augmented by transiently elevated geothermal gradients during the Alleghanian orogeny. Mesozoic cooling histories are spatially heterogeneous and record Triassic to Early Jurassic exhumation, with age discontinuities across the Rideau Lake fault, consistent with fault reactivation and differential unroofing during Pangea breakup. We demonstrate that the Frontenac Arch did not remain a long-lived low-relief feature, but instead experienced significant burial, inversion, and exhumation during the Phanerozoic, consistent with similar thermal histories from studies in the Ottawa embayment, the St. Lawrence platform, and the Adirondacks. These findings highlight the broader significance of the Frontenac Arch by establishing its complex thermal evolution as evidence of its role as an actively evolving intracratonic structure. The arch’s dynamic history contributed to the modulation of sedimentation along the southern Canadian Shield and offers new insights into the tectonic and stratigraphic development of intracratonic regions.