177-4 Reconstructing the Drivers of Exhumation Within the Canadian Rocky Mountain Fold-Thrust Belt Using Low-Temperature Thermochronology

Session: Chronology of Orogenesis: Unlocking the Timelines of Mountain Building

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Abstract:

The Rocky Mountain fold-thrust belt (RMFTB) in Canada has been a key locality for understanding geometries and kinematics of thin-skinned deformation. Despite its role as a global analogue for fold-thrust belts, questions persist regarding the timing and duration of deformation. In part, this is because exhumation associated with RMFTB deformation has been subsequently overprinted by Eocene –Miocene unroofing and more recent glaciation. To resolve the timing of shortening in the RMFTB, we applied low-temperature thermochronology to major faults across the Rocky Mountain fold-thrust belt within Jasper National Park and the surrounding areas. We present zircon U-Pb, zircon fission-track (ZFT), and zircon (U-Th)/He (ZHe) data from the hanging wall of nine faults which cut Proterozoic to Cretaceous strata across a ~145 km west-east transect. One sample from the high-grade metamorphic Omineca belt to the west of the RMFTB yielded a ZFT age ~100 Ma and a ZHe age ~20 Ma, interpreted to record mid-Cretaceous ductile deformation and early Miocene extensional exhumation of the Omineca belt. Samples from the Main and Front Ranges yielded ZFT ages ~230 – 100 Ma which record Triassic rock cooling, possibly linked to subduction initiation, and mid-Cretaceous shortening in the RMFTB. The Main and Front Ranges yielded associated ZHe ages of ~ 60 – 30 Ma which we interpret to record the final early Eocene stages of thrusting and/or onset of extensional exhumation. Within the Foothills, thrust faults yielded ZFT ages ~360 – 100 Ma with associated ZHe ages ~110 – 60 Ma. We interpret these dates to reflect Cretaceous RMFTB related shortening, as well as the presence of unreset zircons. Thermochronology and associated thermal history modelling supports protracted rock cooling from the Triassic to the Paleocene in the southern RMFTB, which we interpret to reflect long-lived shortening. Our data supports Triassic cooling across multiple domains, possibly linked to Triassic subduction initiation along the margin of the Canadian Cordillera, which may have played a larger role in the evolution of the RMFTB than previously recognized. We find evidence for Cenozoic exhumation in the RMFTB, consistent with regional studies that document large-scale erosion that post-dates shortening related deformation. We suggest that RMFTB propagation was directly linked to orogen-scale development, recording protracted shortening as well as extensive post-orogenic erosional unroofing.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7332

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