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Topic

Thermal and Exhumation History of Quesnel terrane: New Low-Temperature Thermochronology Constraints and Implications for Copper Preservation

School of Earth and Ocean Sciences

Date & location

• Wednesday, March 25, 2026
• 9:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Ruohong Jiao, School of Earth and Ocean Sciences, ̽��ϵ�� (Supervisor)
• Dr. Dante Canil, School of Earth and Ocean Sciences UVic (Member)
• Luke Ootes, BC Geological Survey, Ministry of Mining and Critical Minerals (Outside Member)

External Examiner

• Dr. Dawn Kellett, Geological Survey of Canada (Atlantic), Natural Resources Canada

Chair of Oral Examination

• Dr. Darlene Clover, Department of Educational Psychology and Leadership Studies, UVic

Abstract

The preservation of shallow-crustal porphyry Cu systems is a fundamental challenge in tectonic geomorphology, as these deposits typically form at narrow paleo-depths (1-6 km) susceptible to rapid erosional removal. The Quesnel terrane in the Canadian Cordillera represents a globally significant metallogenic province, yet the post-emplacement exhumation history that allowed these Mesozoic systems to survive remain poorly quantified. This study uses apatite fission-track (AFT) and apatite (U-Th)/He (AHe) thermochronology, integrated with inverse thermal history modelling, to reconstruct the time-temperature (t-T) evolution of the Quesnel arc and its implications for ore preservation.

The data reveal a three-stage cooling history. Phase I (ca. 200-90 Ma): Prolonged residence within the upper crust following Late Triassic-Early Jurassic magmatism, with rocks remaining within the AFT partial annealing zone (60-120°C). Phase II (ca. 90-40 Ma): A pronounced pulse of accelerated exhumation during the Late Cretaceous to early Eocene, with cooling rates of approx. 2.5°C/Myr accounting for 1.7-2.7 km of unroofing. This phase represents the primary tectonic reorganization of the Quesnel terrane. Phase III (40 Ma-present): A terminal transition to thermal quiescence, characterized by negligible exhumation (<0.7 km).

This study shows that the Quesnel terrane remained thermally quiet during the Neogene. Unlike the adjacent Eastern and Western Cordilleran belts, which underwent high-magnitude exhumation (>5 km) that stripped away Mesozoic mineralized levels, the Quesnel terrane remained tectonically stable after 40 Ma. This stability effectively "locked" the porphyry systems within their optimal preservation window. These results suggest that the exceptional mineral endowment of the Quesnel terrane is dependent on a specific t-T trajectory that avoided deep Cenozoic unroofing. This study provides a quantitative framework for assessing the preservation potential of concealed porphyry targets in active orogenic belts worldwide.