EVOLUTION OF EXHUMATION FROM MULTI-METHOD THERMOCHRONOMETRY IN THE EASTERN KLUANE RANGES, YUKON, CANADA

The Denali fault zone (DFZ) bounds the easternmost Kluane Ranges and is a dextral, strike-slip structure active since the Late Cretaceous. Despite dextral motion on the DFZ, the Kluane Ranges have ~1.6 km of relief that likely reflect a vertical component of local deformation. We interpret a ~100 Ma long exhumation history from multi-method thermochronometry as a proxy for vertical strain accommodation. We present (U-Th)/He and fission-track (FT) results from apatites and zircons from 17 samples collected from transects parallel and perpendicular to the DFZ. Mean apatite He and central apatite FT dates from individual samples are ~26-4 Ma and ~110-12 Ma, and mean zircon He and zircon FT dates are ~93-27 Ma and ~137-83 Ma, respectively. Sample spatial distribution, data patterns from multiple thermochronometers, zircon He date-effective U correlations, and thermal history inversions constrain the late Mesozoic-Cenozoic cooling history. The youngest dates for any chronometer are <4 km from the DFZ trace. Southern, near-fault samples require rapid cooling at ~100-80 Ma, ~80-60 Myr of near-isothermal holding at ~160-150 °C, followed by rapid cooling from ~25-20 Ma to present. A low elevation, northern sample collected along fault-strike yields a similar t-T path, but with rapid cooling at ~10-5 Ma. High elevation samples >4 km from the DFZ trace also show a similar cooling history but with protracted mid-Cenozoic residence at ~60-20 °C and accelerated cooling at ~25-20 Ma. Data patterns collectively highlight fault-parallel and large fault-perpendicular gradients in exhumation through time. Late Cretaceous rapid cooling may reflect dominantly contractional tectonism and waning arc magmatism. Protracted Late Cretaceous-Oligocene cooling and exhumation may reflect tectonic quiescence in the Kluane Ranges. This pattern may indicate a period of enhanced strike-slip (vs. contractional) deformation on the DFZ and associated low rates of vertical rock uplift and erosion. We infer increased Late Oligocene-Miocene exhumation rates along the eastern DFZ are the far-field effect of flat-slab subduction, similar to prior work on the central DFZ. Our results highlight the evolving influences of plate-boundary processes on exhumation in transpressive orogens.