Thermotectonic History of the Kluane Ranges and Evolution of the Eastern Denali Fault Zone in Southwestern Yukon, Canada

Abstract

Exhumation and landscape evolution along strike‐slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U‐Th)/He (He), zircon He, apatite fission‐track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within ~26–4, ~110–12, ~94–28, and ~137–83 Ma, respectively. A new zircon U‐Pb date of 113.9 ± 1.7 Ma (2σ) complements existing geochronology and aids in interpretation of low‐temperature thermochronometry data patterns. Samples ≤2 km southwest of the EDFZ trace yield the youngest thermochronometry dates. Multimethod thermochronometry, zircon He date‐effective U patterns, and thermal history modeling reveal rapid cooling ~95–75 Ma, slow cooling ~75–30 Ma, and renewed rapid cooling ~30 Ma to present. The magnitude of net surface uplift constrained by published paleobotanical data, exhumation, and total surface uplift from ~30 Ma to present are ~1, ~2–6, and ~1–7 km, respectively. Exhumation is highest closest to the EDFZ trace but substantially lower than reported for the central Denali fault zone. We infer exhumation and elevation changes associated with ~95–75 Ma terrane accretion and EDFZ activity, relief degradation from ~75–30 Ma, and ~30 Ma to present exhumation and surface uplift as a response to flat‐slab subduction and transpressional deformation. Integrated results reveal new constraints on landscape evolution within the Kluane Ranges directly tied to the EDFZ during the last ~100 Myr.

Innovations in (U–Th)/He, Fission Track, and Trapped Charge Thermochronometry with Applications to Earthquakes, Weathering, Surface‐Mantle Connections, and the Growth and Decay of Mountains

“…FT, (U-Th)/He, and 4 He/ 3 He thermochronometry of basement rocks, sedimentary rocks, and sediments quantify the timing and tempo of erosional and tectonic exhumation in orogens ( Figure 6). In mountain ranges that develop in convergent orogens, these tools lay the foundation to investigate relationships between rapid erosion and surface uplift (e.g., Avdeev & Niemi, 2011;McDermott et al, 2019;Spencer et al, 2019; and many others), propagation of deformation into the foreland (e.g., Gautheron, Espurt, et al, 2013;Lease, Ehlers, & Enkelmann, 2016;Thomson et al, 2017), rapid Quaternary exhumation (Blythe et al, 2007;Shuster et al, 2011;Valla, Rahn, et al, 2016;Yang et al, 2018), and Quaternary climate influences on sediment storage and erosion (e.g., Lang et al, 2018).…”

Tectonic Underplating and Dismemberment of the Maclaren‐Kluane Schist Records Late Cretaceous Terrane Accretion Polarity and ~480 km of Post‐52 Ma Dextral Displacement on the Denali Fault

“…Ca. 30-20 Ma (Figure 12c): The Oligocene and Early Miocene marks a major change in the geology of southern Alaska and southwestern Yukon, which involves the onset of exhumation in the Alaska Range and the Kluane Ranges (Benowitz et al, , 2012(Benowitz et al, , 2014Lease et al, 2016;McDermott et al, 2019), drainage reorganization (Benowitz et al, 2019;Brennan & Ridgway, 2015;Finzel et al, 2011Finzel et al, , 2015, onset of Wrangell volcanism (Berkelhammer et al, 2019;Brueseke et al, 2019), and development of the St. Elias fold-andthrust belt (Bruhn et al, 2004;Pavlis et al, 2012). Contemporaneous events in our study area include the post-32 Ma reactivation of the Valdez Creek shear zone indicated by cooling ages and brittle deformation features, development of an imbricate thrust system along the southern flank of the eastern Alaska Range (Valdez Creek, Broxson Gulch, Airstrip, and Rainy Creek faults), and retrograde metamorphism of the Maclaren schist (Waldien et al, 2021).…”

“…It is important to emphasize that the tabulated separation estimates consider only the active strand of the Denali fault. We recognize the likelihood of an older Denali fault system, which may have had multiple strands active during the Cretaceous (McDermott et al, 2019;Miller et al, 2002;Wahrhaftig et al, 1975). Herein, our use of the words Denali fault refers to the active strand of the fault, which appears to have been a single highly localized strand for much of the Cenozoic (Cole et al, 1999;Regan et al, 2021).…”

“…It is not necessary that these basinal assemblages were linked as a single basin system at the time of deposition (e.g., Hults et al, 2013); however, the similarities in depositional setting and interpreted provenance within the Wrangellia composite terrane do suggest that they together represent a regionally extensive clastic marine sequence linked to the paleo-eastern margin of the Wrangellia composite terrane. An Early-to-mid-Cretaceous phase of strike-slip faulting may have translated the marine sequence relative to the Wrangellia composite terrane (e.g., Gehrels et al, 2009;McDermott et al, 2019;Mooney, 2010;Yokelson et al, 2015), yet the displacement history for that structure remains unclear. 5 and 7).…”

Late Oligocene–Early Miocene Detachment Faulting in Crystalline Basement, Mecca Hills, CA, Documented With Zircon (U–Th)/He Date‐eU‐Visual Radiation Damage Patterns

“…Increasing radiation damage in zircon manifests visually as increasing crystal discoloration and opacity (Holland & Gottfried, 1955;Nasdala et al, 1995Nasdala et al, , 2001Woodhead et al, 1991). Selecting grains that represent the range of visual metamictization has been demonstrated to yield a >1,000 ppm eU range within zircons from a single sample Flowers et al, 2020;McDermott et al, 2019). Studies that applied this visual metamictization approach were able to characterize the relationship(s) between date and eU, and thus the low-temperature thermal histories, from their zircon He data that would not have been evident had only the most pristine grains been analyzed Flowers et al, 2020;McDermott et al, 2019).…”