HEMATITE (U-TH)/HE CONSTRAINTS ON SYNCHRONOUS DEFORMATION, HYDROTHERMAL ALTERATION, AND SURFACE UPLIFT IN THE EASTERN DENALI FAULT ZONE, YUKON, CANADA

Documenting evidence for coupled deformation, hydrothermal alteration, and topographic growth in orogenic belts remains a challenge in tectonics, structural geology, and paleohydrogeology. The Kluane Ranges in southwestern Yukon are bounded by the dextral eastern Denali fault zone (EDFZ) that hosts a variety of exhumed fault rocks. We complement previous work documenting 30 Ma-present regional surface uplift by examining temporal relations between outcrop-scale faulting and hydrothermal alteration using scanning electron microscopy (SEM) and (U-Th)/He (He) thermochronometry of hematite-coated fault surfaces from the EDFZ. SEM images show fault surface hematite comprises foliated, high-aspect ratio ~30x300 nm hematite plates with local S-C geometry. Foliated plates are mutually cross-cutting with hematite-quartz-calcite-clay cataclasite and veins of non-foliated hematite at high angles to the slip surfaces. Thirty-eight single-aliquot hematite He dates from 11 samples range from 11.5 ± 3.2 Ma (2σ) to 3.4 ± 2.2 Ma and define date populations at 7.7 ± 0.4 Ma, 6.2 ± 0.2 Ma, and 4.2 ± 0.2 Ma. Grain size measurements are consistent with a hematite He closure temperature of ~60-70 °C, similar to the apatite He system. Hematite He dates are 15-20 Myr younger than previously reported apatite He dates from wall-rock overprinted by hematite fault surfaces. These date relations preclude an exclusively exhumational cooling interpretation for hematite He data and instead suggest hydrothermal hematite alteration at depths shallower than hematite He closure (~2 km). Hematite He dates are from foliated microtextural domains that we interpret to have formed at low strain rates with likely negligible He loss. Cross-cutting cataclasite and hematite veins suggest episodic, possibly higher strain rate phenomena including local fluid overpressures. We interpret our data as a record of hematite formation from ~8-4 Ma, followed by fault reactivation along these discrete slip surfaces via a range of deformation mechanisms and during on-going regional surface uplift adjacent to the EDFZ. Interpretations collectively suggest potential connections among semi-continuous versus discontinuous deformation, fault-related hydrothermal alteration, and regional surface uplift in the EDFZ.